Hello, I didn't see anything in the rules about re-opening old threads and this one is interesting due to widely varying opinions. For my 2C, I would say using backing tracks depends on your circumstances. As I am buying BIAB very soon I went ahead and joined the forum.
Firstly, I am an amateur vocalist / rhythm guitar player (non-Japanese) living in a remote region in Japan. We have a local music scene here, some paid as well as a good number of open mic gigs / unpaid music pub spots where you can just go and perform. These open mic / unpaid venues are the ones I am interested in. I have been trying for about two years to put together a rock / pop cover band , but with very limited success. There is the interest, but there always seems to be a reason not to practice or not to attend a scheduled mic night - some legit (working / family commitments etc.) and some not so much (shampooing the dog etc.). Either way, the band thing is not happening as quickly as I like because we don't practice and we dont get better (e.g. playing in the right key would be great). As we want to do western covers, on occasion i have to explain who people like the Rolling Stones and Springsteen are (for example), as the other band members may have only ever heard one or two of the most well-known songs, which further slows down the process. There are a few cover bands here, but many bands don't have a vocalist as they are unwilling to sing in english (especially if I am in the audience), so it really becomes a complete 'Empty Orchestra' or 'Kara-Oke' experience by definition. There are of course lots of Japanese rock / pop bands for Japanese rock etc.
Jazz gigs (paid and unpaid) are also very popular here and really seem to resonate with Japanese audiences. For other genres (country / rock), professionals (both actual and self-appointed) tend to frown on using backing tracks in any performance, which also tends to limit the material you might hear to the same Dylan / Beatles / Clapton tracks getting played over and over again (I have lost count of the number of times I have been asked to do 'Tears In Heaven'....)
I have a lot of tracks I would really like to do at these open mic nights for which there are no professional backing tracks anyway. So instead of waiting for the right band members to come along, I figured I may as well put together a semi-acoustic set of the songs I want to play. In this case, I consider backing tracks crucial. BIAB appeals because of the range of styles available coupled with the proficiency of the musicians and being able to flesh out known tracks to support guitar / harmonica / vocal to being able to dabble in ideas for different styles / tempos for other songs - from standards by Bob Dylan to a bluegrass version of 'Rio' by Duran Duran

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Either way, in this situation BIAB offers the opportunity to demonstrate what it is we are trying to achieve and hopefully allow us to rework the BIAB tracks back into live backing once we are all on the same page. The other option is the very real possibility of not improving and not playing at all if it depends on putting together a band that may never eventuate.