It's dangerous. People with bad technique are more likely to get hurt or hurt others. The stacked, controlled body position makes it much easier to absorb and react to unexpected terrain and snow conditions and generally stay in control.
A solid foundation will also help you progress much faster. I'm friends with a number of very good racers, and I've gone in the park with some of them and watched them learn stuff in a single day that takes jibber kids an entire year. They're in there stomping 7s first day because they know how to ski already.
Like Ozzy here, I skied moguls for a bit growing up and that gave me a great foundation, but I lost some over the years. Two summers ago I did some race training and generally brushed up on my technique, and the next winter I found myself skiing pow much better than ever before. It made a huge difference and boosted my confidence a lot.
I think some of this loss of technical ability is due to fewer soul shredders coming up. A lot fewer skiers, especially park skiers, grew up skiing nowadays. Instead they watch x games at 13 and head straight to the park. The involvement is awesome, don't get me wrong, but they'd progress faster and safer with real skiing ability. And there's no reason it can't be learned alongside park.
You know why Jonah Williams and Quinn Wolferman are next level good? They're better skiers than most coming up right now. I've known both of them since they were still young beans with Wasatch Project hiking in our summer park. They already knew how to ski fast and ski well then, and you can see where it's taken them.
TL;DR: if you wanna become nasty quickly and safely, learn how to ski well.