Why do weight lifting programs tell you how many reps to do?

Question

I thought that to get the best gains from lifting, you have to work your muscle to overload. Why not just do every set to failure and adjust the amount of weight based on your desired results? Such as low weight for toning and high weight for mass. I just started lifing again after many (5) years and want to know the best way to go.

Answer 1

If you don't do the proper amount you are just tearing your muscles down and that's no good. If you are not doing something right waht is the benefit of doing it at all.