Marsh,
I do weigh and segregate my brass in either 50 or 100 round lots. Keep in mind that Im usually dealing with 250-500 piece lots per rifle. My reasoning is that if the external dimensions are the same, and the weight varies, then the internal dimensions must be different. This must have some effect on pressure, thus velocity.
Now, Ill be the first to admit, that seeing this difference in weighed VS un-weighed brass on paper or a target is hard to do. The benefits, may indeed be minimal, but since confidence is a factor of shooting well, I consider weighing my brass time well spent. With an electronic scale it only takes a few minutes to do an entire lot anyway and I consider it part of my normal brass prep routine.
I then index my brass using a clock method to keep my brass lots identified, orient my case when sizing, bullet during seating, and finally my cartridge during firing.
IE: 45 2.4" LOT A, 201.3-202.1, 12:00 (index mark position)
The index marks (and lots) also give me a way to track brass usage, trimming and annealing.
Some of the brass Ive worked with has been extremely consistent to the point that weighing really IS pointless. Ive had a couple batches of Starline 45 2.4 thats only had a variance of 2.4 grains total for 250 pieces which equals a 1.1% variance. I still weigh it though, because Im going to use the lot method to track other stuff, so weighing is a reasonable way to segregate it as any other.
Hope this helps,
Chuck