Quote Originally Posted by Flying Pig
ALWAYS ALWAYS ALWAYS sally out on bthe first turn of a seige. No matter the odds, if you don't severly botch your play (ie, let the enemy in) the worst defeat you can recieve is a draw as the foe has no seige gear. If you are going to die horribly, do so before the gates of your city although a bloody last stand in the centre is good as there is no retreat from there.
Why do this?

You probably have a relief force on way, with real fighting potential rather than a defensive garrison, with no real chance of victory.

One reason to sally is to capture & destroy the siege gear, if it's not built yet you have less to gain and give up a strong defensive position so most likely suffer unnecessary casualties. And you are opening the gates, and fleeing units may be followed.

Then fighting when highly outnumbered is likely to cause disproportionately high losses, making subsequent defeat more likely.