If you can play properly there's no need to use MP3 or other pre recorded backing.
I play in 2 top clubs and have been resident at both for 5 years now.
I appreciate that we should embrace technology and I do myself. I use Cubase etc for producing backing tracks for many singers and bands on the pro circuit but I will only use my backing to show off at the beginning and end of my nights playing.
I play live to singers who come up to me and give me any piece of music that they want to sing to. I don't know what they are giving me so I have to rely on the score which is often wrong but you can improvise if you don't know the song or if you do know it, you simply play and accompany them. I also transpose in my head which I find easy rather than using the transpose keys on my G1000 and SD1. I prefer quality styles and sounds anyday over all these fancy gadgets such as MP3 playback. I also refuse to play to any midi file at all. I have yet to hear one that sounds half decent by any manufacturer. Each to their own, it would be a boring music world if we all adopted the same styles of playing and taste lol - Keep it live as much as possible