Currently, using one of your companions on a governor slot is a bit of waste compared to having them in their own party or running a caravan to make you money. Maybe it would be a bit more desirable if they would take troops from the militia and garrison to stop people from raiding your villages? It would give smaller parties another set of targets to fight that would be somewhat (with militia) inferior to lord parties. It would allow another way to (slightly) weaken a strong garrison. And players wouldn't feel leased to their land to prevent them from being raided by the AI.