A lot of those things it blocks allow macros, which are against the rules. And GameGuard isn't the only thing the leaves behind hidden files...
Oh ok, so it blocks my anti-virus because it
could allow macros, and ATI tray tools, which is important for my video card.
Also, it is obvious that there are plenty of things that leave behind hidden files, but GameGuard is one of the worst because even if you decide to
uninstall the game, the stuff stays, and it still sucks processing.