I HAVE done the show-car circuit for over a decade. Because they WERE show cars, the engine compartment never facilitated a full-blown high-pressure flush!
I do however apply the same cleanliness standards to my regular vehicles. It helps tremendously when trying to locate a leak, or discovering a problem and proactively repairing it.
If I procure a vehicle for the first time with a grimy engine bay, it gets an engine cleaning solvent with a followup hosing off at the local car wash with the hose set to "spot-free rinse" pressure. Never at high-pressure rinse! Besides the already mentioned problems with moisture on electrical components, the spray is powerful enough to knock terminal connections and vacuum hoses off. You may not readily see the dislocation occurring, and the resulting performance problems could plague you for days.
Engine washing can be done at home with a garden hose when washing off kicked-up road dust and bugs. DO NOT wash at home if using engine cleaning solvents, since that and associated gunk being removed is not environmentally friendly. The DIY car wash bays are set up to reclaim and dispose of the harmful chemicals properly.
I too have had some engine washing results not come out perfectly, but with experience, you learn what NOT to do with your particular vehicle.
Careful with the straight four or six configurations with the spark plugs mounted vertically down the center of the engine. Even though it's shrouded, enough water can make its way in and form a "lake" around the plugs. This won't help it's performance at all, until you can "Wet-Vac" the area. (Yep, I did that many years ago to a 72 Fiat).
I've had technicians tell me that the cars with the pristing engine bays get preferential treatment at the service facility. Probably in the same manner that an attractive-looking woman (unfairly) gets instant attention and better service than a less attractive one.
Besides, if your engine compartment could not tolerate water, you couldn't drive it in heavy rains. So your car is equipped with some protection from water. So wash away! But with care...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car