sedating would be better... like I said, know your doses and you could potentially do it, if need be
For my betta, when I had to do it, it was on two parts: caudal and dorsal. She had to get used to not having all fins, but she could swim.
In similarity to amputating all fins, if need be, it would be closest to a fish getting his/her fins chewed up - either from fin rot, or another fish. I had Reggie and Shiloh, both who had been attacked and their fins a mess, or non-existent. It was hard for them to swim, or at least navigate around corners and turns....
If one were to do this, on all fins, the larger the space the better (to avoid infections that would come easier in a smaller space that collects ammonia faster), however, they'd need to keep it shallow enough for the betta to reach the surface if he had troubles swimming
just my input =D
edit: not for the faint of heart, and not for fragile-immune-system bettas. Last you need, is a very very sick betta to get more sick from stress, being out of water, and (another) open wound.