12 is so heavy, it's really hard to wire it to light fixtures.  J boxes for switches get so crowded, no room behind sconces, etc.  The current drawn by lighting is so low, 12 gauge, 20 amp circuits are just overkill.  I would wire all outlets with 12 and use 14 for lighting.  The electrician is the one that has to deal with it, so if he wants to use it, let him.