Re: "P" = Park; Why need handbrake?
most handbrakes in road cars do not use a clamp on the rear brake disc like for eg a ferrari's. instead it is a "drum brake" on the inner side. This is true for almost all bimmers except models like M5. I believe normal road driving will never endanger any part of your wheel/brake if you pull the handbrake after a day's driving. At least not to a significant level. Otherwise the newer model's autohandbrake thingy will all pai.
However, the increased temp while tracking at sepang, if you pull the handbrake, or similarly, instinctively holding on to your footbrakes after you pit in, will cause your pads to smoke out, or even catch fire. On normal road driving, almost never.