Morrus said:... more to do with PC actions during a large battle or war while the battle takes place around them, and how the battle progresses due to their presence/actions.
This is something along the lines of what I do.
I've seen a couple of problems with mass combat rules for D&D games:
The first is that they're typically a separate enough rules set that there's a learning curve issue. The player must become adept with these new rules before the character can be a solid leader, but the character is the type to be a solid leader before the campaign starts using these rules. It is a case where the player isn't as good as the character should be.
The second is that it typically only interests a couple of the players, and usually takes up a lot of time. A major battle can chew up an entire session, during which time the folks who don't feel like playing war games are bored.
So, I tend to slide PCs into more "elite units" roles rather than behind-the-lines commanders. The battle becomes a setting for several encounters, and the results of those encounters have effects on how the battle turns out. Then, everyone remains engaged, while still having an impact on the battle.