engine bay simplification

Hi i was wondering what some people have deleted out of their engine bay for simplification, with no problems other than the CEL and emissions. I just want to get an idea of what's been done and just cause im asking dosent mean im going to do it, I come from the world of 1.3L Mazda rotary engine where its common practice to get rid of everything expect engine and a huge turbo! I wouldnt do this to my daily driven BMW so im just curious



Thanks