I've used it for some math concepts. The memorized concepts give you something to mentally play with, and give anchor points on which you can build more knowledge.
Sort of? It depends on the "thing", but spaced repetition is pretty standard for physical activities like martial arts. In essence, you're attending a class that focuses on drilling a particular technique on a regular interval. There isn't much research from sports pedagogy, though I think its more because its just a "known" requirement that doesn't require much new research. However, I would also say that spaced repetition goes beyond simply reviewing Anki flash cards and that there is an element of kinesthetic learning that is necessary to strengthen the learning gains.
I use it for encyclopedia entries and general glossaries, which I gather from PDFs or just online. There is IMO no better way to learn a topic than to memorize an encyclopedia about it.
To give some examples, it's used heavily in US med schools, and I achieved great academic results using it to study CS in university.