https://www.youtube.com/watch?v=z3cjTqCQemUnot to be the cynic but i would be careful messing with those if your not certain of how it works. I can't say for certain in this case but the "-1" value is usually used to tell the system to use all cores whereas any positive number would tell it to use a specific number of cores. Of course, i can't speak to the hows and whys of your specific experience but just thought I'd point that out so people know to be careful.
-0 would be to use all your system cores, depending on how the games coded im pretty sure, but in most games a "-0" means to use all of X (In this game X being cores)