The advantage of keyless over a blank is a functioning light. Why the NEC has the requirement, I don't know specifically if it is for protetion from fire from what some clever people might do to get light, or if it to minumize the hazards of fumbling through a dark room. But for whatever the reason for the code, there is exposure to the hazard until the lights get picked out, ordered, delivered, and installed, which could be a long time. Mix some small kids in and who knows. Are ther bigger things in life to worry about, sure, but I don't think it is unreasonable to require a keyless. As an installer, I wouldn't leave a house for final with just blanks.
