I have only basic ASL and am by no means an authority. But I think between native ASL speakers its use would be very rare, mostly just to clarify an exact spell

I have only basic ASL and am by no means an authority. But I think between native ASL speakers its use would be very rare, mostly just to clarify an exact spelling for something that was going to be written down in english. Native ASL speakers who are completely illiterate in english certainly exist, and I'm not sure at all if they know or use finger spelling.