As long as your a patient man, there is no issue, and you will help reduce scar tissue. But, if your pushing harder on the plunger (because your hand is cramped and its been 3 min since you stuck and its getting uncomfortable, for example) then IMO you can actually create more scar tissue when using a smaller guage needle then compared to using a normal size (say 23 ga). Think of a garden hose and a large pile of sand. If the water flows out of the hose at "slow to normal" rate then the sand gets moderatley displaced. But if you put your thumb over the end of the hose then you the sand gets blasted out of the way and displaced quickly. The thumb over the hose is you pushing hard on a 27 ga pin, the oil is being forced out at a higher rate will actually cause more scar tissue than a larger 23 ga pin with low pressure.
thats how I always thought of this issue, and no I dont have any medical studies or published reference material to back it up. But I think the garden hose in the sand example "keeps it simple".
If your truely patient, then yes you can use a 27 ga pin, take a long time to stick, and theoretically end up with less scar tissue.
"my 2 cents"