It may be most who do it when the family is not home but not all. A story came to mind a couple of years ago where a family was murdered in Penn. during a robbery. Most families are always home in some form and some thieves have short patience when it comes to what they want. An intelligent thief would use this information like this to their advantage.

The most famous story is of the Clutter family written about by Truman Capote. I'm not sure if they had a gun but the family was home and were intended to be murdered at the time of the robbery.