Honestly, not too necessary. If you need it then you're in dire straits already, and it's vulnerable enough that you'll probably be KO'd anyway as long as your opponent tries. Although, in my actual experience, most of the time they do stop, assume you're dead, and comment about how surprised they are when you make it back (which feels pretty good), but it'll only be so long until knowledge of Luigi's recovering abilities (and how to completely nullify them) becomes common.
I'd compare it to Falcon's moonwalk or Sheik's Shino-stall. You could probably be a high-level contender without it, at least until PM reaches 20XX levels. It's not a fundamental part of play, but it does expand and improve your options. If you're real good you can use it to vertically follow people after using your second jump, if you're confident enough you can drastically increase your off-stage edge-guard range, and simply being able to stall with it is a useful mixup. It's also one of the rare things in Smash that can be practiced alone (in other games, even!), so there's no reason not too, especially since it requires real exercise (not just experience) to maintain. And now's such an early point in the game's life with so much possibility to discover, how can you not want to try to be in the forefront?
EDIT: Oops I thought this was the PM section. Yeah it's like pointless in Melee.