Any hard fast movement of an item with any amount of heft to it, coming to a sudden, abrupt stop against another item with any amount of heft to it, will eventually wear down both parts, generally the one with lesser heft being damaged sooner/faster. I wouldn't trust some guy in some video to decide what's "safe" for my $200 phone.
I've been known to flip it shut a time or two, but gentler is always safer. That said, how long do you want it to last in the first place before you *need* a replacement?