I'd guess the consensus is that any "help" it provides is unnoticeable.
How could you tell if it helped?
Those that do it feel better for doing it, and that's OK by me.
As far as I know it can't hurt anything.
Drive fragmentation in general isn't a noticeable problem unless it gets really excessive, but many defrag religiously and feel neglectful if they don't.
Modern CPUs can blaze through the registry very quickly, fragmented or not.
If you feel better after you do it, do it. Whether it helps in any measurable way is another question entirely.