In Asia, a lot of people believe in dry cupping when you start to feel like you're getting sick. People can deride it as pseudo-science, but enough people think it works that there may really be something there. It's like Traditional Chinese Medicine; it works but is not as consistent or well understood, so it seems very hokey. The reality is that it works, but we don't fully understand why.
I did dry cupping once just for the experience / hell of it, but it was years ago and I don't even think I was sick at the time. It was hot and uncomfortable. Not terribly so, but I still have no interest in replicating the experience, especially since matches are involved!
I do guasha every once in a while when starting to feel flu-ish or a cold coming on, and I do think it works ... somehow, but you have to catch it early.