By injecting the pressurized air back into the compressor housing, when you let your foot off the gas or shift, the released air pressure keeps the turbo spooled instead of slowing it down with the pressure drop. I understand what you're saying about not having a MAF sensor, but DSMers who do have one don't just recirculate it to keep their fuel curves right, they do it to keep the turbo spooled. It makes the turbo not have to work as hard to re-pressurize the IC and pipes when you mash on the gas for the next gear. So basically even without a MAF, it improves throttle response and lessens turbo lag.