Have you ever used ngen.exe?

Question

Has anybody here ever used ngen? Where? why? Was there any performance improvement? when and where does it make sense to use it?

Answer 1

As an addition to Mehrdad Afshari's comment about JIT compilation. If serializing a class with many properties via the XmlSerializer and on a 64-bit system a SGEN, NGEN combo has a potentially huge (in our case gigabytes and minutes) effect.

More info here: XmlSerializer startup HUGE performance loss on 64bit systems see Nick Martyshchenko's answer especially.