Again speaking generally (not necessarily about Mercedes) most modern engines are calibrated for EGR and disabling it does NOT help the engine. In fact, it can cost you fuel economy, again because the engine is calibrated for it. To properly remove EGR involves changing the cam, reprogramming the computer (at least in Otto-cycle engines), and other smaller mods (thermostat temp change, etc.). Sometimes even the compression ratio is tailored for EGR.

On our older Diesels I suspect that removing the EGR probably helps keep the intake tract cleaner and lowers intake temp - always a good thing. I do not have EGR on my 617 in the S-10 but it is race-only and will never see a mile of road duty. As stated, local and state regulation will effect the legality of that mod.

An interesting tidbit - on Otto-cycle engines installing a high-overlap cam (common in performance applications) ADDS EGR in a passive manner. In areas that accept an exhaust test as proof that an engine is "clean" it's one of the things that is done to lower NoX - and it works. Coupled with an oxydizing cat to clean up HC and CO (like the generic CATCO cats available from Summit or Jegs) and you can pass almost any car assuming that the engine is in good condition.

Dan