"MORE" is a helpful sign to teach your baby. Before they can actually speak words, they can communicate with you that they are enjoying something and would like MORE! More milk, more food, more bubbles, more of a silly game etc! Singing this song (over and over... and OVER!) while doing the sign for MORE will help your child associate the word "more" with the sign.
Another tip to teach your child the sign and concept of "more" is to give your child a little of their favorite food and then say to them, "Would you like MORE? (while doing the sign language for "more") Then give them a little more of their favorite food. (We did this with blueberries and oranges with my son, but for awhile we think he thought the sign for "more" meant "delicious fruit!" LOL!) I was a bit worried that if I taught my child baby sign language they might depend on it and that it would hinder their speaking, but this is in fact not true. It actually is shown to help them develop language!