I never lock the bathroom door unless the grandchildren are in the house.

As for outside doors - if I am alone, they are locked.
Rosie, I think it is a very good idea to have a strong lock - bolt lock - on your bedroom door. I had never heard of it before until one saved a friend's life. Her father had always put bolt locks on all the bedroom doors and put one on her's when she moved out.
A rapist broke into her house through the sliding door (locked), took a knife from her kitchen and proceeded to try to open her bedroom door. She woke up and saw the handle turning. Then he tried to force it and finally tried to kick it in. The bolt lock held. She had a gun in the bedroom. The intruder heard her call 911 and got out of the house, dropping the knife in the hallway. She didn't have to use the gun.
The police told that the rapist had been in the area and injured some women. They didn't put it in the newspapers - bad publicity, I guess.