Originally Posted by big_swede
Right about the squat and deadlift. Those are the "dangerous" lifts and should be executed with proper form. Dipping the bar just a bit while squatting is ok imo, as long as back is arched.
The total back arch in deadlift is not a must for me as long as it is more arched than bend forward and that it stays tight.
Right. What I meant is that there are some exercises where a certain form must be used in order to lift any kind of heavy weight. You're never going to deadlift a lot by simply walking up to the bar and trying to heave it up without knowing how.
There are also certain things, like a back arch in a squat, that are just no-brainers. Your back can't support 500 pounds bearing down on it without flexed and tight back muscles.
On the flip side, it's not going to kill you to do a kip in one of your pull-ups at some point; or use some leg drive on a particularly heavy press. I think most intermediate/advanced lifters have enough sense to determine where and when they should or should not cheat.