I could think of a dozen reasons...
Because he wants to use a sharp pin
Because he has extras of one or the other
Because the vial is big and it's easier with the 1.5" but not so easy on his delts
etc...
LMFAO! . I always draw with one pin and poke with a new one. I use the same drawing needle a few times. I thought you had a question regarding the length of the needle...