There have been a lot of threads started about this, Look in the "Detailing" section.

And to answer your query, I have kept every one of my engine compartments as clean as I can! It makes working in there easier, looks better, and if you, god forbid, must take it to someone for them to work on it, they might respect your vehicle a bit more. Or see in advance that you are concerned about the little things and will do the job clean and correct!

Best.