[jcp123]

Not efficient? I thought Harleys were some of the most fuel efficient bikes, comparing to any model's direct competitors

My guess is that it's some kind of holdover from the old, pre-synchro days of rev matching. People got used to it, did it on their bikes, and for one reason or another it stuck around as some vetigal thing they do for which nobody knows the reason aside from...doing it because they've always done it.