I can almost assure you this doesn’t cross the mind of 99% of techs or mechanics...There's one good reason to clean the engine. If you take it to a mechanic for repairs, they'll see a clean engine and everything is shiny, you have a better than average chance of the job being done right. It's psychological. If the customer keeps the engine this clean, obviously, he's detailed oriented. I've done that with my 03' Matrix and each time the mechanic has mentioned how clean the engine bay was.