DonDon said:
Stopped at traffic lights which have just turned red and so will be a longish wait, if on level ground, doesn't moving the auto box to 'P' make sense?
If you want to do it, do it.

Why not?
That said, I've driven and been driven in cars with automatic boxes in the US, most of Europe, the Middle East, the Far East and Australia and it's not common practice. People switch the engine on, put the car into gear and - apart from reversing et cetera, of course - leave it there until they switch the engine off.