The standard joke is that P stands for Professional or Perfect mode. Actually on Pentax, it's great! Pentax has the Hyper Mode where the front wheel adjusts the diaphragm, the rear wheel adjusts the shutter speed. Combined with the “proper” AutoISO of a range ISO100 to ISO800, you are all set. It's fast and very good, close to excellent.
So back to the Professional mode. This weekend, for the first time with Canon, I used the Perfect mode. It's not bad! Perfect? No. Professional? Depends on who you ask. It has a strong tendency toward the higher shutter speed and the wider aperture. Not too bad of a choice, I do the other way around, normally I'm in the A, for amateur or aperture, and let the Canon set the shutter speed.
It's spring, and the goose will attack anything that moves click on image for gallery
This was taken in the professional mode: 1/400 f/10