bazilisek: I'm still not quite sure what this initiative is good for. GOG installers are self-verifying, and the extras are in zips, which also have integrity control by design. Why the extra layer?
(I'm not trolling or trying to insult you, I honestly don't understand.)
3 Reasons:
1) So that you don't have to run the installers when you buy many games at once (say, during promos)
2) So that you can automatically test your collection against future corruption.
3) So that if GOG does future updates on game files, the MD5 of future download won't match and anyone running the utility will come bitching here about it and let us know that there was an update (at which point the utility can be updated with it).
My utility also cut-pastes GOG downloads in a neat directory structure, but that's just additional gravy on top.
I know I always hated doing it manually.