Bilingualism is more than just having communication skills. Research suggests that it boosts brainpower.
"It's almost as if the monolingual child's brain is on a diet and the bilingual child's brain stretches to the full extent and variability that Mother Nature gave it to use language and exploit human language." -- Dr. Laura-Ann Petitto (Gallaudet Today, Spring 2012, p. 18.)
Many people express their concerns about it. The truth is that there is no evidence that bilingual acquisition leads to confusion, nor that bilingual acquisition leads to language delay. Rather it benefits brains.
Hearing people fear that using a signed language in deaf children will hinder speech development. Studies show no evidence of this. In fact, studies show that deaf children acquiring ASL as a first language at the earliest age learn English (specifically written) as efficiently as hearing children.
Bilingualism opens up a part of your brain. It helps with many mental tasks like problem solving. It helps you see or think in a different way (e.g. intercultural perspectives and alternative solutions).
Harlane Lane, et al. "Bilingual and Bicultural Education for Deaf Children." A Journey into the Deaf-World. California: DawnSignPress. 1996.