It is not immediately apparent but there are 3 completely different issues which get rolled into this topic of basing though often only 1 or 2 are really germaine to any given project. It is no wonder that the question gets clouded, especially if one is looking for a universal solution.
What are these issues? I summarise them as follows:
a) Practical: Economy of Effort vs Flexibility
b) Esthetic: Static Diorama vs Moving Diorama
c) Theory: Element Statistics vs Counting Noses.
Lets start with the practical side. It doesn't take long pushing 24 or 48 man units of individual figures about to appreciate that some form of movement tray would make things easier. Over the years two main methods of speeding movement have been adopted, the temporary movement tray, often large enough to hold the whole unit or a large segment of it and the smaller permenant stand with various figures mounted on it. Easy. Now how do you change formation and mark the effects of combat?
With some foresight it is usually possible to arrange things so that the width of the smallest stand is acceptable as the width of the narrowest legal formation and so on. What if you want to split off part of a unit? or deploy a unit in either close or open order? or fit the stand into your terrain? Sometimes it is possible to arrange a convention, for example, saying that 2 close order stands with a gap between them now represent the unit in open order. A lot depends on the design of the rules and often rules designed on an element basis (see below) will provide conventions and flat out forbid some things. The question of terrain becomes one of design or of acceptance, as in ruling that a stand in the middle of a small fort is actually manning the walls. With individual figures, these issues generally don't arise but it does take more care and time to move them, even on temporary trays and of course, if that flexibility is required then they have to "debus" and leg it on their own individual bases anyway. The pros and cons balance out in my experience.
The esthetic question actually has a 3rd side which I will mention then dismiss, some gamers don't care one way or the other so it becomes a non-issue. For those who do care, the most evident are the modellers who delight in making each stand a little mini-diorama, the wounded soldier supported by his comrade, the panicked recruit being grabbed by grizzled centurion and so forth. Some of these can be near works of art, others of us produce much more modest attempts but which are still fun to build. The thing that came slowly to me is that once done, they are fixed whether they are appropriate to the current situation or not. If loose figures are used, the gamer with time in hand and imagination in gear can advance his skirmishers from rock to tree and can artfully arrange his troops in rout or pursuit or make a suggestive gagle as the men file onto the bridge of boats or wade ashore to assault a foreign shore. The result will not be as definitive as a mini-diorama but rather more suggestive of a child at play but in my experience, some individuals can retain that imagination through the decades, or rediscover it.
A phalanx advances, leaving a trail of bodies as graphic evidence of the effects of massed Persian bowfire. One could do some casualty vignettes to get an even better effect.
Finally we come to the red herring, the question of Elements. Briefly, I am using this term to refer to rules that treat a group of figures or "element" almost as a gaming counter, it has set characteristics that are used to determine the element's effectiveness and capabilities. The figures are only there to lend colour and perhaps take up space. This often requires either a roster or some form of markers though some rules, like DBA, manage without these. The other main alternative, is to use the figures themselves as markers, typically the number of figures is used as a factor in determing combat effectiveness and figures are removed to show casualties, loss of cohesion and so forth. In its purest form, the element system treats each group of figures a discrete unit but it is common to find hybrid systems where a number of elements units are grouped to form a unit. In some cases these elements are then treated almost like individual figures rather than as true elements.
Why do I call this a red herring? Well, at one time I believed that an element system required figures to be fixed to bases of a set size and that nose counting systems required the ability to remove casualties. Anyone who has seen a casualty cap in use or used a roster can give the lie to the latter belief and I suspect it was was really a disguised prejudice against such things. The realization that fixed bases are conducive but not essential to element based rules was one of those head slapping revelations that occurred to me while agonizing about how to arrange a game designed for fixed elements when the troops that were going to take part were being supplied by three different players, each with a different basing system. Essentially if there is agreement as to what constitues an element and an amicable spirit of fair play then it doesn't matter if this group of hoplites are fixed to a base while that group are all individually based, as long as everyone understands that the group of individuals is an entity, has the same characteristics as it would if glued to a base and has to act as such.
The Persians, 4 60mm x 40mm bases of 6 figures making a comfortable, easy to handle, unit with 3 formation options. The Carians are crammed in 8 to a base of the same size, a feat not possible with individual 25mm figures, not if you want them to be stable. Looks great at the start but partway through, uh-oh giant dunce caps! Well, I could have used pebbles or dead bodies but.... The hoplites they are fighting are using an emperimental deployment with a mix of 4's and 3's and singles, a failed experimental deployment.
So what does this have to do with my Persians? Well, they started life under a nose counting system with a mix of multiple figure bases and single figures, the worst possible system imaginable!. They were later rearranged into fixed 60mm wide elements, 2 deep for infantry, and fought as such under various element style rules where noses weren't counted and no casualties were marked or removed until the whole unit died. Without changing their basing, they went on to fight under WAB which assumes individual figures and thus, casualty caps or marker dice came into play. Practical but ugly and worse, my stands were poorly arranged and my tactical options were limited unless I started down the path of figures moving sideways in amrch column or others being placed in odd or illegal formations while I asked my opponat to please imagine that how they were supposed to be deployed. In the short term, this was acceptable but once the decison was made to resuurrect 25mm ancients gaming as a major part of my hobby, a better solution was needed.
Two reasonable alternatives presented themselves to me: re-adopt an elements based set of rules (and either convince my friends to follow me or else put up with the irritating limitations when not playing solo) or rethink my basing system. After examing every system that I had come across or used myself over the years, and after allowing the taste for toy soldiers that has resurfaced during the last 10 years, I decided to go with the WAB standard of individual figures on unit movement trays but using a frontage and organization that will still allow me to field 60mm wide elements when I need or want them.
The 1st Regiment of Immortals in their yellow caps, all smugly arranged in straight rows on standard sized bases. Beside them, wait, that guy in the middle doesn't even have a base! But they are on a standard frontage and could claim to be an element if required, base or no.