My son's band was very successful, but they had ten members and an agent and had to split the income so much that the band members couldn't survive. They went down to four members and a well-programmed keyboard - the only member of the band with a female name. Seems to work quite well for them.
So, I think if the backing tracks are a wisely-used supplement to the live performance, they can be a great asset if used well (and they don't require you to split the pay).

-Joe-