The answer is simple.
Sign Language can help a child communicate before their bodies are physically capable of speech.
Babies as young as 6 months old can learn to sign.
In fact most children begin communicating with sign language. They wave hi and bye, point to things and put their hands up when they want to be held.
Babies know what they want and teaching them sign language as way to communicate can:
Increase the parent/child bond
Increase vocabulary and IQ
Develop fine motor skill
Help build receptive language
Be a fun way to learn!
Based on all these benefits, why wouldn't you want to teach your child to sign?