I have heard from many, that it would as stated free the engine up to rev easier, but believing that & then trying it until that high compression head & cylinder started breaking case studs off, I reversed my thinking & put that head stay back in place.
I had thought, by the head stay being in place, that if the frame flexed/twisted any it would in turn stress the head & cylinder & cause gasket problems, but with it in place, I've never had to replace a gasket because of it being there, not in all my years of dealing with 250Rs.
Neil