I switch off the fuel and the battery kill switch every time I leave my car for more than a few minutes. It's just a routine that I've got into. I've never drained (run) the fuel out of the carburettor and have never experienced any problems from not doing so. My routine on my boat is different, there when I've returned to the marina part of my routine is to disconnect the fuel line and wait for the motor to stop. Thinking about it I probably do it for a couple of reasons:
1. I might not be using it for a few weeks.
2. I used to have two stroke outboards and with them there can be real advantages of leaving the carburettor dry.
Running the car until it stops from fuel starvation may not be necessary but it certainly won't do any harm.