If you're not experiencing crashes or video memory exceeding limits, you don't need to touch this. All it does is set a limit for memory usage for the game - total system VRAM * memory scaling value. Set it too low and its going to be swapping textures from your storage far more often than it should, which will harm performance.
Reducing the memory scaling significantly improved the campaign mode for me. Without it I was getting stutter and freezing every couple of seconds.