The range limiter on the 70-300mm G SSM has 3 positions, (Full AF), (Infinity-3M) and (MF). The first and last are self explanatory, the middle one is as I said above and limits the focus travel from Infinity down to 9 Metres. Some other lenses I have with focus limiters have a low and a high setting, which works differently. The 70-300 has an SSM motor and it doesn't go to infinity and back to get a reference point like non SSM lenses. I think.
Sony A7, A850, A77, A700 || Sony>> 70-300G, 28-75 f2.8 SAM, 16-80CZ, 50 f1.4, FE 28-70 OSS || Minolta>> 300 f4 G HS, 200 f2.8 G HS, 100 f2.8 (D) Macro, 50 1.7, 28 f2.8, 28-135 f4-4.5, 70-210 f4, 500 f8 Reflex, TC x 1.4 HS, TC x 2 HS. || Sigma> 21-35 f3.5-4.2.