Yeah, occupy if same culture or if it's already small. I don't try to enslave too many cities at once if they're going to all go to the same few governed cities in order to control overpopulation. I just alternate with exterminate. Some times I need the initial infusion of income over the long term benifits of higher population.

Basic rule of thumb is don't do anything that will deplete the population below roughly 2000 people.