Pretty sure that’s Morgan doing vocals also

Well, most obviously, deaf people can understand the lyrics when there is a good translator. Deaf people (like many hearing people) often enjoy music by feeling all of the the various kinds and levels of vibrations and moving in response, often along with other people also moving in response to the same vibrations, whether heard or felt or both. If you think about concerts these days, a huge portion of the experience for sighted people (whether deaf or hearing) is visual. A great interpreter, like this one, also conveys a lot of the feeling, tone, dynamics, etc., of the music in her facial expressions, gesture sizes (bigger = louder, to take one of the simplest aspects at a very basic level), ways of moving (smooth vs staccato, joyful vs sad vs sexy vs raging vs ..., etc.). And of course there are myriad social aspects to going to a concert with people who share some of one's tastes and feelings. Given how much other noise there often is and how much better one can hear the music at home with current technology, I imagine that very few people of any kind are at metal / hip hop / rock / pop / dance music / etc. concerts primarily to hear the music. And a sign-reading person who can see the interpreter clearly (on a screen or on stage) is likely to be get the lyrics better at many concerts than someone who can only hear them, especially with an interpreter this good!

I met him, and the rest of the band at rock fest. Great guy

Years from now, her kids will ask Mommy if she was a rocker.