I would say that if a person has really good form, a fixed crawl might increase his accuracy at the new point on distance. However, since there is a gap between the fingers and the arrow nock, any form errors will be amplified. It is important to hold the bow at the same cant, or zero cant, for each shot. I tried this for a while and decided to return to my regular hold. I prefer a more relaxed way of shooting. YMMV, of course.
I don't think you need to have ILF limbs or tiller adjustment to use a fixed crawl. People were successfully string walking years before those things came in vogue.