Originally Posted by Paradox
The quads are very, very involved in raw squatting and deadlifting (especially squatting). There's this notion lately that the only thing involved in a squat is your posterior chain.
And again this is a relatively new concept, you're looking at the last 10-15 years, prior to that a lot of the big guys would do Leg Presses quite regularly. If you look at old Deepsquatter articles you'll see a lot of references to them.
They're also very handy for doing uni-lateral work, takes the balance aspect out of the equation. Uni-lateral work in itself is quite useful.