by Rex Dart
Something else I didn't see mentioned is that selling a building is a free action.So if, for example, selling the Sawmill for 7 gives you more benefit than owning the Sawmill would, you can do it, AND you don't have to forego some other action to do so.
Actions are the scarcest resource in the game, and anything that can provide you with a benefit without using one is at least worth thinking about.