It’s rare, and often spoke about in cryptic ways because it’s illegal in basically any use-case unless you are using your own personal copies - that you yourself copied - from your own original. At least in the US. Quite honestly, the only thing that has kept the emulation community online so strong is a near lack of enforcement.
That’s why everyone lost their mind a few months back when Nintendo sued one particular site into oblivion, and then several other major resources voluntarily shut their doors. It was almost unheard of for it to be enforced to that degree.
(Frankly, I blame the rise of the Raspberry Pi device. Everybody and their grandma’s dog was selling them outright with the pre-filled libraries, and when Nintendo tried to make it’s own version the LOUD consensus was “that’s stupid, just build a pi and download the roms”. …way to stay on the down low people…)