Pop-pop is a fuel or exhaust issue. (Flooded needle valves can soak the spark plug and allow unburnt gas into that exhaust stream, where it will ignite and make small random pops. Exhaust leak pops are usually louder, and they sound like the Kiddie Racers in their chromed-out bugs cruising down the main drag on Saturday night.) No well-tuned carbureted Volkswagen will pop without the emissions devices.
As you let off the throttle suddenly as if panic stopping, the airflow halts immediately, but the fuel flow due to vacuum is still high. This creates a highly rich condition, which is bad for the environment (unburned fuel = released hydrocarbons, if you care about these things,) and bad for fuel economy, (and you probably care about this.) The throttle positioner grabs the throttle arm as it's about to snap 100% shut, and holds it slightly open to let more air pass through and retain a slightly more stoichiometric mixture of air and fuel. (Bentley spec holds it open around the equivalent of a 1200 RPM idle for 3-6 seconds. Not much!)
Because the positioner systems hold the throttle butterfly open a tad, yes it reduces engine compression braking. BUT there are tradeoffs beyond the air/fuel metering!
In my bus, I like to take my time with the 2-3 upshift. Since the linkage is, I don't know, twelve feet long I can allow my shift to be slow, (allowing the synchronizers to speed up gently,) and kind to all moving parts. By the time I've declutched, meandered on over to 3rd, and am releasing the clutch in 3rd gear, the engine speed is kept higher and matches the input shaft with the output shaft of the transaxle. For this reason, I call this device the "throttle positioner" to those who care about the environment, and I call it the "shift enhancer" to everyone else.
For those that REALLY need more reasons to run them, watch a CHT gauge on a flat level stretch of freeway. Cruise, for example, at 360* for a minute, then declutch into neutral and let the engine idle while coasting. BAM temps go up at first, then slowly down. The combustion chamber heat always permeates outward through the head, but now with the cooling fan spinning four times slower, the heat creeps out. Some people call it heat soak, and it's most pronounced after hot shut down. By adjusting my throttle positioner to hold a faster idle for a few more seconds than spec, I'm trading a TINY bit of the fuel saving benefits for a reduced thermal shock to my heads, which I think is worth it.
Six times my allowed soda intake for the night… Somebody get me a Bosch caffeine regulator,
Robbie
It's holding up nicely all over the muffler, and the tailpipe will only look like garbage if your Felt-Not-Cork valve cover gaskets decide to dump your oil all over the tailpipe before coming to rest on Interstate 5. 
Mark had to new 2nd and 3rd gears, new synchro's and swap in some unbent shifting forks to get it back to working smooth again.