If you only lift off, you may not produce enough vibrations in the string to generate a clean sound. You could get away with lifting off if you'd pick the string but in legato, you'll probably loose sound. I guess with enough gain and effects it can be done.

I always pull-off. I do most of my legato practice with a clean sound (no distortion) to be sure that I generate enough vibrations. If you can do a good legato with a clean sound, it's gonna sound really good with distortion.

Well, that's my 2 cents anyway..