I think any decrease in turbo life is small on a tuned car.  There are plenty of OEM applications that do not use any kind of vac reservoir or electronic control of DV, and some have no DV at all.  My preference is very strong springs on big boost cars for driveability  Throttling the turbos on trailing throttle gives better response than any DV setup, but at a cost.

Rick

Whether the car is tuned or not is irrelevant.
The reason why they are there is to improve turbo life and increase fuel economy on lower load areas.
On high load, especially if revving the engine high, they do pretty much nothing, as at high revs the vacuum generated by the engine is more than sufficient to pull a dump valve with even the strongest spring wide open.

A part throttle example with N249 attached. Note no spike and boost dropping much quicker, no surge occurring.
Not an S4, but it looks the same on the S4 as well ... and my RS4.
This example is especially nice because it is a BAM engine, so stiff dump valve from factory.

Many many modern cars dont have fancy valves/ecu controlling the dump valve.  Look at the early AGU/ARZ motors with no N249....Ive never known a turbo to fail/lifespan be shortened by running no valve.

From what ive read/understood, people often get part throttle 'dumping off' where the N249 is opening the valve on part throttle causing a jerky drive.

When the throttle plate is closed, the DV is instantly in vacuum, (you dont see a boost gauge taking half a second to stop reading boost pressure to vacuum pressure)  The boost helps keep the valve closed, vacuum opens the valve.

Its like all the other crap that comes attached to the later 1.8T engines...SAI, EVAP, N249, charcoal canisters on all models.  fact is, the motor runs perfectly well without any of them in situ,

AGU has softer spring on stock dump valve. Your reasoning is also ridiculous - as it was said before, the lifespan IS shortened by running no dump valve (which you are essentially doing at part throttle with a stiff spring), it is universally accepted that violent stalling of the compressor causes high load to be applied to the shaft and the bearings of the turbocharger. Have you disassembled even one turbo? Do you have any idea what goes on during compressor stall?
Wrong, this part throttle jerkiness is caused by bad tunes. On a properly tuned car there is no issues whatsoever with things interfering when they should not. The N249 never ever opens unless there is a negative pressure gradient (only exception is huge overboost). On a good tune there will be never a negative pressure gradient during constant throttle application.
Incorrect, on lower engine speeds the vacuum generated by the engine is not sufficient to open valves with stiffer springs, such as the 710N. Especially since the load applied from the side of the diaphragm is actually helping keep it closed.
The only thing that I agree removing with is SAI - this is only there for emissions and warming up the catalytic converters quicker, but as a side effect bore washes the engine during every cold start.
By removing EVAP you are turning your car into a potential fireball during a crash, as your petrol tank is full of very explosive fumes all the time.

But hey, clearly what you read on forums is all true, and Bosch has no idea of what they are doing, isn't it?
Your only arguments so far have been "everyone else does it", "there are cars without it". By making such remarks you just make it look like you understand absolutely nothing about forced induction engines and turbochargers.

The only thing up for debate is just how much turbo lifespan is reduced by running no dump valve - many opinions on this one.
But:
a) N249 does not interfere with anything, unless your tune is utter crap
b) Removing the N249 causes pressure spikes and increased amounts of compressor stall.
c) Compressor stall (also called surge) has a detrimental effect on the bearings.

These are the hard facts about it. Fact is also that the Audi Rally team ran no dump valve of any sort on the S1 - thus the characteristic sound, but they could also afford to fit a new turbo for every race.
Any kind of MAF setup with a closed-circuit PCV will also not take kindly to this, as the air will travel backwards inside the intake during compressor stall and oily mist will land all over the air filter and MAF causing incorrect operation of the MAF.

If your only argument for it is the shorten life span of turbo, AND the measurement of that decrease of life span is negligible, then the the reasons to get rid of it out weight the reasons to keep it.

 

Did you read what I wrote about the MAF fouling?
Bosch also says it improves fuel efficiency, which makes sense, as pumping losses can be reduced by keeping the valves open in some situations when no boost pressure is desired, allowing to hold the throttle wider open as opposed to choking the engine with it.

As to whether the effect on the turbos is negligible or not, well that's the only thing that can be debated.
But please list a single reason to remove it? It does not weigh anything and takes almost no room. They also very very rarely fail.

yes ploz. Need help finishing ME7Sum :/

I meant ME7Sum