I don't know about long term, I have always been worried about spraying cold water on a hot engine or hot exhaust manifolds and making them crack. I am sure the chances of cracking the block or heads is pretty slim, but the manifolds I am not sure.
What I always do is cover up my air filter ( if it is exposed at all ) then leave my hood open to cool the engine off some while I wash the rest of the car. Then I use the degreaser ( when available ) or high pressure soap. when finished, I rinse with clean water, then shut the hood, and rinse the hood, fenders, and windshield off again because crap from under the hood often flies up on those spots.
Not sure if this is the GREATEST thing to do, but I do it..... I am sure someone else will chime in also