One of my observed cases was a 6.0L PDS (VT365). My buddy picked up a solid 2MPG deleting the EGR. Apparently, on the Ford's, you could just unplug the EGR and despite the EGR position sensor obviously not reporting the valve functioning, it didn't throw a code. The ECM just acknowledged the EGR wasn't working and continued on, at least that's my understanding of it (it wasn't my vehicle). Thought it was interesting.
Correct me if I'm wrong, but my understanding of EGR on a gasoline engine is that under low load, exhaust gas, which is inert, is allowed to blend with the air charge, which facilitates both the reduction in NOX and allows for a leaner mixture with more timing (improving efficiency).
Given how much broader the enrichment range is for a diesel, and the fact that you don't have to worry about spark knock, I don't believe the same benefits, at least nowhere near of the same magnitude, are attained. It's mostly for reduced emissions with the side effect of introducing much dirtier exhaust, due to all the soot, into the system, which shrinks intake ports and causes build-up. Diesel EGR also needs to be cooled, resulting in the fitment of EGR coolers, another problem/failure prone item.