Poorly tuned instruments are generally outlawed by musicians. However, some tone friction can create an interesting touch, give a more natural texture and bring an instrument a little more into focus without straining the mix – of course, it’s all about the right balance.
The western trained ear perceives tunings outside the usual scales as interesting. It has happened to me more than once that I took an acoustic guitar out of its hibernation that had been parked for a long time and played around with the strings for half an hour before finally tuning it.