I agree with Wheatfield, but ...
I can see at least one situation when an experienced photographer will use the Green mode. In emergency, when we need to take very, very rapidly a shot within a very, very limited timeframe, I would switch to the Green mode to ensure that I will not stuff up the shot. That has happened to me before: I forgot that I set a particular setting that was unsuitable for this one-in-a-million chance shot. I was very, very angry after myself and I am still pissed off ....
Now I use the Green mode in emergency and I would only switch back to P-mode if I have the time to double-check my settings.