I find this thread fascinating.
None of the bands I am in (3) use backing tracks, and I never have, and agree with the guy that said the day he has to, he will hang it up for sure.
When I'm out wanting to hear music, I want to hear live music, whether that is rock, jazz, country, bluegrass, reggae, or dance music.
I was on a cruise recently. 2 party bands on board. 1 was a male/female duo playing guitar to backing tracks, one was a 4-piece band with a chick singer playing everything live.
The Duo room was empty every night, the live band room, while never packed, had so much energy there, that band was so much more entertaining. So I think its not just me that wants to hear it live. Otherwise, IMO it cheapens the experience FOR THE LISTENER.
A big part of the reason why people would use them, as has been mentioned here, is personnel issues - you want to keep the numbers low to make more $ individually, and you can't find the right people to play X for 1 or 2 songs a night. Well I have to think that if you can't find the people who play, you should pick another genre to play. As one of the few keyboard players that also plays bass, I feel bad that good keyboard players are so hard to find. If keyboard players are hard to find, I should never lack for work. Which is pretty much the case, but not always.
Being a keyboard player in a classic rock cover band, I'm asked to play all the signature licks in the songs that require organ, piano, or horns. I know how some of you feel about keys playing horns, and until I got my Korg Kronos, I always felt the horns sucked, but now they at least sound legit. We don't play Baba O'reilly. We don't play Pink Floyd with all the crazy sound effects. We could play those, I could obtain the samples, but we would rather stick to something that we don't have to compromise on. Just like we don't play X song because its way out of our singer's range, or we refuse to play Free Bird. Whatever, you have to make choices, and some of them may not be popular with your audience.