A: To get better at our sport of choice.
I did heavy cleans and speed squats today. I felt pretty spent after the squats but I tested my vert (along with basically everyone at CP) and jumped a couple 33's before a couple 34's and a 34.8''. Not too great but pretty awesome considering all the work I had done before. I finished it up with some heavier (225lb) sled pushes. I am working mainly on the initial push and first couple steps, as my top end speed is pretty good but I need to learn how to accelerate more powerfully.
My weight is up a bit again, but I just need to keep eating more. Tomorrow is a day off, and I'm back in for training on Monday again.
So remember, your squat, deadlift, or bench don't matter unless you can use that strength to your advantage in your sport (unless you're a powerlifter in which case it works out anyway--you're welcome, Dan). On the other hand, if used properly in a smart training program, there is nothing that can help you get faster and more powerful than strength training.