Here's another perspective:
I scan my 35mm negatives at 3200 dpi, and my 6x6 negatives at either 3200 or 4800 dpi, depending on whether it's color or B&W. The reasons? I like to spend my time scanning only once, and archive the negative as soon as possible;
The other one is (most important one), I like my negatives: most labs have high turnout, and the operators could care less if the negative they're handling is from Aunt Pat or Henri Cartier-Bresson ("Henry who?" they'll say), will give them back with fingerprints and scratches galore. If I'm going to have the lab print a picture, I resize my file, and put it in a memory card (I gave up with CD-RWs after I got them back with --you guessed it-- fingerprints and scratches) and have them print the files from there if their kiosks are a pain to use (some of them are).
I realize not everybody can do this; I put together my own system and have four harddrives, and have room to expand for two more, all rather "cheap" because I guess being a closet geek pays off.
So scanning big files can have its benefits. I just hope I don't have to begin building a backup storage rack next year!!