If you've ever atteneded a pistol match you'll quickly see who does and who does not practice their draws when the thumb safeties come out. All too often a good shot will forget to turn it off and you know they've never practiced drawing their gun from the holster.
I shot USPSA with my M&P and IDPA with my Ruger SR9c. Not only is it a pain to remember to disengage the safety, I also have to remember to rack the slide after a reload with the Ruger.
M&P with no safety and built in automatic slide release for me!