It the owner's preference. Personally I think people should leave their guns unchambered unless they know they are about to use their gun. It's just safer.
Sure, sure. "It takes longer having to rack the slide" but sometimes that's all you need to get rid of a threat. The sound of a gun cocking can be enough to stop certain threats. In case it doesn't, you then have a bullet, in the chamber, ready to use, if you need to.