Drop me in the "micro-managers basket" and call me obsessive, but I prefer not to leave anything in the hands of the AI other than the AI factions...

It might be a character flaw, but I actually enjoy raising and lowering taxes....and I like the fact that a wrong decision (in terms of how far I push the local populace) can result in rebellion against the tyrant....oh dear, that would be me...

As for merging units, well sometimes I will do this if the enemy are likely to be attacking a province held by a battle weary army, but generally I prefer to re-train and re-equip units without merging, on the theory that 2 really good experienced units are better than one great unit....