The people you meet that are deaf only need you as an interpeter or someone to speak for them in an emergency situation. It is not a language that is needed on a daily basis that will benefit you for a job, such as spanish does (unless you are working with deaf bosses). Second disadvantage is that the American Sign Language is not speaking english but rearranged english that is not normal conversation to the average hearing person, as it states
http://researchpaperwritings.net/and
http://www.dartmouth.edu/~news/releases/2002/nov/110402a.html. It is hard for a hearing person to learn to talk "backwards" learning their language.