Tell us about yourself!
This is terrible advice. I'm a seamstress, and you should NEVER cut the fabric off any pants you are hemming. For one thing, if the person you are hemming the pants for is still growing, they will be SOL and you'll have to buy an entire new pair of pants. Secondly, it ruins the jeans, and if you mess up the length, you'll be screwed. Instead, remove the original hem, measure the correct length you want to take up, make sure the measurement is accurate all the way around, and sew away. I've hemmed about a hundred pairs of pants. It's not the "easy" way, and it can be time consuming, but you'll be saving yourself a huge headache in the long run.