For me at RTW BI most funny is with the Romans! Its easy with factions that have horde option! But the bad thing in BI is that sieges are so GAYYYYY.... Realy hate those big cities towers which kill like half or more of your army untill you get to the fucking center! I mostly had fights at open field, and sieges just go with 2/3 armys and wait the end of their food and they go out and fight, where is easy
Well, Historically, sieges were risky bussiness, and they had to be done swiftly and properly, otherwise you risked losing your army to famine (not with proper logistics of course) disease, or defences.
And yeah, starving out defenders was pretty common scenario, but you couldnt pull that off unless you had enough provisions to keep your army sharp and going.