I like to think of the British Army at the beginning of the 1775 scenarios as a "Seed Army". Most of the units have only 1 or 2 subunits and therefore aren't really ready for primetime campaigning. I've found that by keeping them out of harm's way and allowing them to absorb replacements can turn that Seed Army into a Mighty Tree Army over time.
I wish the British AI would not just blow out of Boston at the first opportunity in 1775 when it is just too small to defend Boston while trying to subjugate the entire northern regions. I find that playing as the British it's far better to hang out and wait for those mighty 1776 reinforcements before going out and about capturing new cities. Although the American AI is bad at allowing it's army to be trapped and wiped out in Newport, it's very own "Yorktown".
I've heard from many game programmers that it's better to have a busy AI but I've always thought they were way wrong and their overly busy AI's provided little challenge. I'd like to see the BoA AI's be made better so that they sit tight and repair damaged units and absorb replacements during the winter and then campaign during the summer campaign season. Warfare back then was a seasonal adventure and the game should reflect that in the way the AI's operate during different weather states.
Omnius