It depends who is skier/golfer you are talking about, and it depends what kind of error or "error" you are talking about.
Let me explain this now. If it's about top level athletes (skiers, golfer, tennis or basketball players, it really doesn't matter which sport it is), then yes, these "errors" are made intentionally. Each athlete has his own technique which helps him be faster, better, more accurate... This technique might be way off the "proper" by the book technique. In competition sport, it doesn't matter how you look (unless we talk about ski jumping, skating and other sports, when you have judges giving grades for your "look"), but how fast/good/accurate you are. For me, one technique gives me a bit more power, a bit more speed, while for you, completely different one gives you same results. So with top athletes, "errors" are intentional and they are done to be faster.
Different thing are hobby skiers/golfers/runners... Noone of them is chasing extra hundredths of a second, so they don't need to optimize their technique with "intentional errors", just to be faster (except for few, who might have to do this due some disabilities which would otherwise prevent them from doing particular sport). For such people, I doubt they would be doing errors intentionally. Such people, at least in my opinion, do errors, because they don't know better (sorry my English is far from perfect, so this might sound bad, even if I didn't mean it bad way). And I'm pretty sure, they would love to change this, to have "proper" technique without such errors, if only they could.