The basics kicks, punches, and other techniques look like they can really come in handy, but the forms after black belt just look a different way to apply those techniques in a non-practical way.
I'm not much of a "forms guy" myself these days, but the reason for training in a school isn't just for new forms, it is for training partners. I've never met anyone who just trained alone in their backyard by themself who was any good. Solo training is a portion of your training regime, it can't teach you timing, it can't teach you the pain of sucking up a shot and keeping going, it can't teach you sensitivity, and it can't measure progress. Practicing alone will not make you awesome at self-defense.