Chris,
I've used them (and not) off and on. In low light, they can be an asset to see where the hit was IF there is pass thru or deep enough penetration to put the nock near the hide. If there is poor/little penetration the lit nock away from the animal doesn't help me see the entry point. They help in recovery IF they stay lit, and some don't. I believe that their use would prohibit Pope & Young entry of an animal if you're lucky/inclined to kill a P&Y critter.
Overall, I rarely use them but if you're after those South Alabama hogs.......
Good hunting,
Todd