Is out sieging the AI an effective tactic?

[Slen]

I was playing around with this today...had the virtue as my pretender, the winged race(I can never remember the name heh), she had 8 air, 4 nature and 4 astral.

I had her and a few nature mages I was able to pick up make a very large number of wine bags..... I started off in very poor positioning on the map BUT I was able to quickly get a large number of castles... not sure why the enemy didn't fight me much initially but they didn't.

Is forcing the enemy to waste time sieging your city, while you actually have a positive food production inside effective, or sieging a city for so long the populace starve, or do you think it takes so long that the diseases are not worth it?