QM or Quadrepedal Movement is a broad term. Any time you've got all 4 limbs down is considered QM. Crab walking, crawling, cat balancing. They're all QM. I would recommend incorporating many types of QM into your conditioning regimen as the benefits are innumerable. In conditioning aspects, QM is great for strength training in the arms, core, and lower body, balance, grace, speed, and learning to use all four limbs simultaneously. In actual use with parkour, the benefits become obvious in rolls, landings, just about every vault, getting low quick, and plenty of other situations.
The nerve connections you're making in your brain when doing QM gets your body less inclined to simply follow the dull pattern of "left foot, right foot, left foot, right foot" and more inclined to do whatever you want it to. Hands and feet can work in unison while doing totally different things. It's beautiful really. Dim Monk is a good example of drawing on QM a lot in parkour. Just search him on youtube and his 2005 and 2006 vids should pop up. He doesn't do a lot of straight forward QM but you can tell some of his movements mimic or draw upon QM basics.
Just train as much QM as you can. Most of the time staying low will give you the most in terms of conditioning. Good luck!
