I often take up the middle of the lane at stopping intersections so that I get a turn in the queue and I have direct visual communication with drivers, and to eliminate at least one of the potential conflicts at the intersection. (Right hand turners from beside/behind in your lane.) I sometimes use a car in my lane as a "blocker" if I'm convinced it's not turning to help shelter me from other potential conflicts. I generally ride with aggression and quick acceleration in these situations.

If no one is behind me, I also take the middle of the lane to avoid doors. When someone is behind me, and I'm not riding at the speed of traffic, I get the fuck out of the way and I let them through, being cognizant of the proximity to doors, then bump back to the center until the next potential passer. This is courteous, costs me basically nothing and keeps everyone traveling efficiently. On gridded streets with stops at every intersection, this is usually a non-issue because cars don't have the distance to exceed my speed anyway. I'm not afraid to assert my space in the middle of the lane when it doesn't impeded anyone, but I also make effort to be courteous.