I am not a very strong singer. People might not want to hear me singing so much. I wonder if Jeff Beck was a busker if he would need/use backing tracks. I am sure he would use them instead of singing, as would Blackmore, Malmsteen and many other i am guessing.
If i want to present myself as a 'guitar player' like a quite-type, lead guitarist who knows lots of cool solos and can improvise, then why do i need to stand there and sing with an acoustic guitar, struggling with the carpal tunnel syndrome in my left hand?
What is so wrong using, let's say, a backing track of a Joplin song and i use Janis' voice track singing her song in the backing track? I will be the lead guitarist.
Am i supposed to try to sing like Janis or try to do my own version of her vocal when i am not really a singer? And when i break into the guitar solos, am i supposed to play them to dead air? Maybe someone passing by would like to join my little act. I can easily alter the backing tracks for them to join in, too. It shows other musicians that you can "follow" a song's structure, and follow "a band".