The first group says leave the engine alone, all that accumulating grease and spilled oil keeps everything lubricated.

I wonder just what a gooey film of dirt and oil on the outside of the engine and components would be "lubricating." Last I checked, it was the clean oil inside the engine that did the real work. Any oil on the outside gathers dirt and that is not good lubrication for anything. Plus, it eats away at rubber, causing early failure of belts and hoses.

Of course keeping the engine clean is the best policy. But that doesn't mean that ALL attempts and techniques to keep it clean are without their dangers. You have to make sure that the chemicals are not too harsh, any forced water doesn't blast away any delicate or fragile parts, and then of course there is the cost/benefit equation and the issue of how much time you want to put into the job.