You got to use common sense in my opinion. Some things don't need much and others need a lot.
If I am dismantling the engine of course I clean it up, why risk something getting in. As for carburetors I do like to clean off around that area even on fairly clean engine. Never know something going get missed and fall in cause an even further teardown. A plus side to this is the customers are happier to see a cleaner engine.
Things like oil leaks are a lot easier to find on a clean engine too especially when using a UV tracer dye.
