Depends on what you're up to

*hehehe* ... *oops* that wasn't only inside my head was it
Especially the South with those big fat brigades they have that are almost half a division alone and need fewer CP's than the same number of Union regiments can be used to threaten less disputed areas or just to try to get behind the lines and disrupt communications.
[INDENT]
If you're the Union fighting for Springfield MO with Rolla as your supply base, and one of those brigades comes rolling up out of Ozarks headed straight for Rolla, or St Louis or Jefferson, you will certainly take notice.
[/INDENT]
Of course you don't really need a general to do that, and Athena often sends them without a general; there still a brigade with or without a game-represented leader. They just have their own inherent, generic, characterless leader.
In fact that might be preferred, depending on the leader you might use to lead one of those fat-boys. If you want to do a quick strike on Rolla, a 3-1-1 leader will not do you service. He will diligently give your brigade his 2 CP's. But about half the time he will be inactivated (have the brownies) and not only slow your brigade's movement down by 35%, but also prevent it from acting aggressively
[INDENT]
If the leader's not activated, he cannot go to Offensive Posture {unless entering enemy held territory} and in no way assault a location in any case. On the defensive, however, in friendly controlled territory activation makes no difference.[/INDENT]
Okay, there is a gamey trick to get around this, and ... uh ... *cough*

if the leader is inactivated, just separate him from the brigade and let him march along behind the brigade (in other words, they move to the same region, but each in their own stack). This way the brigade can move at full speed, less the difference for being under-commanded, but will not lose the 35% automatically if they encounter the enemy. If the leader becomes activated underway, just recombine him and off you go.