Army/Garrison Leaders

Not at all . My 2 cents, for what it's worth. Haven't played MotE in a little while now, so memory's a bit hazy, but I think the below is correct. Hopefully someone who's a bit more up-to-speed with the game will meander around the forums before too long.

You definitely don't need generals for forces that you think aren't likely to see combat, and the benefits you get from having generals on a flank, particularly when you can set the tactics, is well worth focussing on your main 'battle' armies. From my somewhat hazy memory, you don't need generals at all for a force to be able to fight, generals just improve the quality of the fight that your force will provide, and allow for tactics on each of the (up to) three sections. If I understand the question correctly, at the end of the day it's a strategic decision which should be based on your particular circumstances, but when I play MotE I tend to focus my generals in the mobile armies rather than garrisons, except in strategic defensive locations.