Do you do any weight training to help your cycling? What do you do, and why does it help?

For example, I read somewhere that muscles have more endurance if they are exerting only a small fraction of their maximum force, so if your quads are so strong that pushing that big gear takes only 25% of their available strength, they will last longer than if pushing that gear required 50% of their available strength. I also read that typically hamstrings are much weaker than quads and do much less work, but if you make your hamstrings strong then they can do their full share. Finally, I read something about using weight training to develop explosive power.

But that's just reading, I have no idea what is actually worth doing. Do you know something about this?