Just as the Topic asks - Every Turn in a Grand Campaign do you:

Save your money and try to have a treasury? Greedily sitting on your piles of gold while the peasants go hungry?

OR do you:

Spend every florin at every turn, constantly providing settlements with upgrades, refreshing troops, creating diplomats, spies, assasins, etc, etc.

I always nearly manage to spend my cashflow every turn, whether it be at the start of a game or even late into the game when you are making tons of cash. Its never enough for me.