Yeah, I guess it helps boost the air density going into the combustion chamber, but that would be primarily for the sake of power output, wouldn't it?
Most of my reading about turbo systems has been about their application to gasoline engines. In those cases, intercoolers boost charge density, but more importantly, reduce the likelyhood of preignition and/or detonation by keeping compressed air/fuel mixture well below gasoline's auto-ignition temperature.
Since diesels don't pre-mix the air and fuel, you can't get preignition or detonation. In that case, I would think that the hotter you can get the air in the cylinder, the more efficiently it would react with the fuel. That is... short of melting combustion chamber components.