You NEED to stretch, otherwise you'll get injured, preventing you from training. Also, being inflexible severely limits the range of exercise/sports available to you. If you don't have proper depth on your squat, you don't get the full benefit of the exercise. If you squat too much weight while your hams are tight, you're gonna strain or tear them, simple as that. It's annoying because stretching hurts, takes a lot of time, and the effects can be hard to see, but still...you have to do it.