I started a thread on the same topic last year: Officially done with mat-slapping forever
I'm firmly in the "no slapping except in breakfalls" camp.
I know this has been discussed in depth, but I would just like to announce that I am officially DONE WITH MAT SLAPPING.
Over the past 14 years I have trained with many teachers, half of whom expect students to roll quietly and half of whom want to hear the thunder after every single throw. I've been flip-flopping back and forth to please whichever teacher is in charge.
Well, now I have my own club and we don't have very many mats. It was crowded and I was demonstrating something to a student during keiko. She threw me off the mats and I decided mid-throw to just go with it, throwing in an impressive mat-slap (partially from instinct).
OW MY THUMB!!!
Okay, so nothing got broken. Okay, so maybe after all these years my mat-slapping technique is all wrong (somebody send Donovan Waite Sensei to my dojo for a free seminar please). But all I can think about is that it is a good thing we were not outside and there happened to be a root or rock or piece of glass where my hand came down. That would have been bad.
Seriously though, my Sensei says my breakfalls are fine. I don't smash the mat as hard as I can when I breakfall, why would I do it during a roll? My students will be learning nice gentle rolls and elegant absorptive breakfalls from now on (assuming I have the skill to teach them). If mat-slappers at seminars think I am wimpy they are absolutely welcome to their opinion.
Victoria Family Aikido