Also, this also explains the whole trimming thing you posted about:

http://www.howstuffworks.com/question100.htm

( Trimming head hair is good for your hair because of the fact that if there is damage, such as split ends, on your hair then that will stop it from tearing more up the strand. It isn't 100% necessary for you to trim your hair in order for it to grow, but it would greatly help the health of your hair :) )