For me, it’s not an issue of single or multi-based. In my opinion, in games we treat each stand (whether it represents a single man, a team, a squad, a platoon) as its own independent, autonomous entity, and so we send it flying all over the map to do as it pleases, rather than having it participate ad but a part of an overall organization.
I believe we do this because we can see the whole battlefield, and despite attempts to introduce uncertainty and fog of war, we are rarely truly fearful of enemy forces showing up in an unexpected place.
The whole purpose of formations, is sub-units working together as a larger unit, is to deal with the unknown, to give the commander the greatest amount of flexibility within the terrain and tactical situations to deal with something unexpected happening.
The use of formations is intended (generally) to provide a reserve, some piece of a commander’s unit that is unengaged and therefore can be used to deal with something previously unforeseen. In our games we can have our Unit A being shot at by the enemy’s Unit X, but then we (as the player-commander) direct our Unit A to essentially ignore enemy Unit X’s fire and move to engage enemy Unit Y. Under normal circumstances (enemy Unit X being on a mountain top three miles away, firing small arms at us harmlessly not counting as normal) this does not happen, human nature is to deal with the folks that are shooting at you. We could talk all day about what-ifs for different scenarios, splitting fire at the squad/team level etc…, but in the overall scheme of things, you don’t ignore enemy units delivering effective fire upon you.
***For purposes of my example we must assume that either enemy Unit X or enemy Unit Y’s appearance on the battlefield came as a surprise to us, as we’d be a bad commander if were asking our Unit A to assault two enemy units.
Anyway, Unit A is going to have to engage enemy Unit X, and we need a reserve, Unit B, to either engage enemy Unit Y and assault them, engage enemy Unit X (effectively enough) to allow Unit A to disengage and move on enemy Unit Y, or lay down fire to allow Unit A to break contact.
This could have been an assault or a meeting engagement, maybe even a defense if we tweak it just a bit, but the point is that we often talk about the commander designating a reserve, whereas mostly in real the reserve is designated by the formation the commander adopted in order to give him the best opportunity to keep at least one element unengaged and thus able to be used in reaction to something unexpected.
I hope all that makes sense.