I've always wanted to know exactly how the CPU bottlenecking the GPU works? Based on some limited reading I've done, it bottlenecks when you're doing something that's more fitted for the CPU (playing at a lower resolution, turning graphical effects off, etc.), where the GPU isn't pushed that much, so the majority is dumped to the CPU.

How would my CPU bottleneck dual 550 Tis, but not a single 560 Ti?