yeah VW were making it run as quiet as possible and using the only lubrication method possible for them, they couldn;'t expect the orioginal buyers of new g40s in the early 90s to spray the right amount of ptfe lube in every 1000 miles or so could they? They also needed a way of silencing the boost return as again, a lot og people paying £11k in 1991 for a polo wouldn;'t be too happy it if was dead noisey.
Personally, I think it is to keep the charger in better order which is the best advantage of this. The proper PTFE lube applied in correct quantities (i.e. 2 or 3 short, half second sprays every 1000 miles) will keep it in much better condition than the horrible watery shite that comes out of the oil breather, ever emptied a catch tank out?
Then the other benefit is that the charger is only sucking in cold, fresh air instead of warm air re-circulating. Colder intake air is always good for power as it contains more oxygen per unit of volume and that allows you to burn more fuel. The difference in temp between air coming back through the boost return and fresh air will be significant, esp in the UK where it's fecking freezing half the time!
You can damage the charger by pouring miles too much PTFE into it but you can also damage the charger by pouring pennies into it, just don't do that and you'll be fine.