Fighting for Cecil and Ignoramus's vote:

I like the draft system because:

(a) they are YOUR troops: they come from your settlements, they are the type you are built training grounds for, with the armour upgrades, experience etc that you expect etc.

(b) you will have much more control over what kind of units you get

(c) you don't have to worry about your neighbours "pinching" your troops from the merc pool

(d) potentially you will get a lot more men, meaning the kingdom is less at risk from a coup

(e) it makes settlements really matter in a civil war - in a long war, people may fight for ground rather than just chasing the enemy army

(f) it makes civil wars very major events for the kingdom - potentially quickly draining its coffers. It will make people less willing to tolerate open conflict in the Kingdom and instead encourage a quick resolution.