Are you asking about those cheap clear plastic things on the spokes (about 2 x 4 inches)? Quite often they are there only for legal purposes. I've seen them loosen, get out of place and jam the wheel. Not a pretty picture. I've seen the plastic seatpost-mounted rearfacing type drop down, jam a wheel and cause an endo on a mtb.

I'm all for using reflective stuff on the bike at night, but use reflective tires when you can and replace the cheap stuff with quality accessories and check the bolts often.