Practically the only reason I do not play on Very Hard campaign difficulty is because that is the only campaign difficulty in which I have noticed the rebels to actually besiege my towns. I don't mind being besieged, but I do mind VH campaign because of the fact that rebel armies can pop up out of absolutely nowhere, right next to a town, and conveniently besiege it. You can never see it coming. So this is why I used to play on H/M.

Now, the reason I started to play on H/H is because it gives the AI armies slightly more strength on the battlefield (oh, and I use Darth's formation mod, tailored for EB). This I only do because it gives me practice in defeating stronger armies, something players like me (of the weaker factions, such as Hayastan) need to increase in skill.

Micromanagement practice is one of my favorite events. All you have to do is give yourself a couple of house rules. For instance, give each unit orders individually. Eventually you'll get faster. Also, turn all skirmish modes and attack at will modes off. Increases your acuteness. Real great if you plan on playing strong players online.