I rent, so I'm mainly concerned that if someone were to ransack the place, and it came out that I hadn't locked the door, then I'd get the blame for the damage

I rent, so I'm mainly concerned that if someone were to ransack the place, and it came out that I hadn't locked the door, then I'd get the blame for the damage and the landlord would try to get me to pay for repairs. As for bikes, I have a fairly nice one ($900 new). I lock it all the time but only to stop crimes of opportunity -- some teenager seeing it undefended and riding off with it. I know (from experience) that bike locks don't stop determined thieves, so I try not to leave it unattended for long periods of time.