Like Archimbaud said it because you need to give some of your possession to vassal (other Lord or make a companion one)
Also a city can hold a 300 hundred man garrison and still provide a profit if you take care of it that it don't get it carravan raider too much, the villager that come to it are not assaulted by bandit and that village those villager come from are not raider. Don't need to be perfect in doing so, but simply trying to do it should generate profit from the town, not including the money you make from doing it. =p
Also remember by 300 garrison I mean a resonable one (bit like the AI control one), not one where you fit 300 Hulscard in it:wacko:, cause remember it only cost about 2k to fill a city with 1000 Swadian militia or Nord footman.
