Bigguy,
Do you move the troffer while it's turned on?
We do this for a living as well, and I think the general consensus has been that although not required, we still use the bushings.
I contacted a couple of manufacturers about this about 2 years ago, and found out that they weren't required. I don't think I've put in 1 piece of cable without them since, tho. [Linked Image]