They change the CRC of the individual rom & bin files inside your zipped Rom. These kinds of things are used with RomCenter, if you say... Want to play your KOF2003 or SVC Chaos Rom on Kawaks or something like that. You can also use them to fix problems (like no sound or weird graphics) with your Roms.
I find it very nice, I knew that site a while ago, mostly when I was interested on NeoGeo hacks and stuff like that. I used to be on the alco's forum at that time, some people there are experts about hacks, patches and NeoGeo, and many others are pretty interested about it: Johnboy, iq_132, etc