Another reason this is not typically done is that large predators need a lot of food, and produce a lot of waste. In turn, water quality may be sacrificed (in particular nitrates). While overall this may be of rather little concern or impact on fish health, it can be very very bad for a reef tank. The two, IMO, are at odds, and while it can be done in some cases, it is not necessarily easy. Like having cake and eating it too....I would go one way or the other. Or try things like dwarf lions or such in the reef.
Do not underestimate the growth rate and size of this fish. And it is not common, IME, to find an LFS who will take back a large panther grouper. If you want this fish, be prepared to keep it for good.