Being a bilingual, trilingual or more, it improves your languages. You can sign with your mouth full. Scuba divers can communicate underwater. Firefighters can talk in the dark and smoke. You can talk through windows of buildings in the long or short distance.
Drivers can talk briefly in any lanes while driving.
You can be sure that nobody can overhear through doors. You can talk and talk as much as you like in a library or church. You can communicate in noisy bars and discos. SL may be beneficial to other people with special needs, such as autism or communication problems. SL can be used to communicate with animals, such as dogs, apes, etc.