I used to not do it, but I have for the last dozen or so batches, and I've been really happy with it. I get slightly better efficiency, have not had a stuck sparge since I started, and it seems to create a better filter bed than non-conditioned grain as the wort I collect has been a lot clearer than it used to be, and I rarely get even a tiny grain particle in the kettle now. I also notice a lot less dust in the air when I'm grinding.
I figure out what 2% of my grain bill is in ounces, and then that's the weight of RO water that I use. I do it in 3 batches, so add a little grain, mist a little water, put the lid on, shake, repeat until I'm done. I then let it sit for 10 minutes before grinding. I usually weigh out my hops in between, so it's not really wasted time.