Always a lot, many japanese author-animator likes it.
Basically happens in every shounen and seinen anime, many shoujo, even some Josei. Especially in fighting-adventuring genre, but became a trope in slice of life and school animes as well. Just. I dont know, JBwolf seems to not do anime cf collections any more. The other guy doing these collections (Marble ? ) seems to come up with his favourites every now and then, one in a quarter year or so, so just wait for him if you dont want to spend your time watching anime series in your free time ^^