If you're using the HMG below 750RPM, are you really using the HMG?

Throughout my 991 hours of playtime ^{holy shit get a life} I've seen many divers using the HMG at the lowest firerate possible, sometimes at 600RPM when just picking it up from a corpse or something, but people using it at 750RPM has been a VERY rare occurrency, at least as far as I could tell when I wasn't busy surviving.

Obviously if you pick it up because you have no other option you're going to go for the less uncomfortable setting, and if you're trying to shoot down a gunship you won't go Rambo with it, but other than such edge cases...

... what gives?

Why would you choose the ohfuckohshitohfuck stratagem and not use the ohfuckohshitohfuck setting when five hulks are chasing you (A.K.A. the ohfuckohshitohfuck situation)?
As far as I can tell THE appeal of the HMG is its insane DPS.