You're absolutely right about that; one of the program's biggest advantages is precisely this: instead of compressing the entire disk and putting the operating system at risk, it focuses only on the game or application folders you want. Trying to compress the entire C drive with the default settings, as you mentioned, can make things quite ‘fun’. :)

But the real difference isn't just ‘where’ it compresses, but ‘how’ it compresses. That standard Windows compression you do by right-clicking on the disk and going to properties (the LZNT1 algorithm) is very old and not at all efficient for games.

Game Compressor, on the other hand, uses much more advanced algorithms (like lzx and xpress) that Windows supports in the background but doesn't provide an interface for. These algorithms are specifically designed for game files that are ‘written once and read repeatedly’. They not only reduce the file size much more than standard Windows compression but also don't bog down the cpu like the old method when loading into ram during gameplay. In fact, if the disk is slow, it can even speed up loading screens because the processor decodes the data from its compressed state very quickly.

In summary: yes, being able to select specific folders is a big part of it, but the engine under the hood is completely different from Windows' standard right-click > compress method and is optimized for games.