I was recently fighting with a complex file. I didn't join everything into a single solid model so I could make adjustments. When I selected all the parts and exported as an STL for CamBam it created a single STL file, but the complexity was an order of magnitude higher because all those internal surfaces were still there. I was fighting memory and processor usage for a day and a half. This is with 64bit CamBam on an 8 thread machine with a lot of available memory. Finally about half an hour ago I went back to CAD joined everything and then exported the STL. After doing an entity replace and deleting the offending entity everything worked crisply. (It was still complex enough that things worked better if it was hidden.)
I admit with CB-64 on this machine I have gotten a little lazy and let the machine do the work. It cost me a day of labor to be lazy this time around. LOL.