[Dean Roddey]

I think that it was said correctly above. The guitarist would know if he needs to use it because it would be part of the tone he wants to get. If you think that he's not getting the tone that's best for the song, then yeh, you could suggest he use one if that would help. But generally, if he's getting the tone he wants, and you just want it more compressed as recorded, then compress it on the way in, I would think.