It's just power consumption.
For me higher performance states on GPU brings me no benefits...so why use them :) I don't need more than 60fps in viewport, even 30 is enough for work.
I'm using nvidia inspector utility where I can disable higher performance states.
Here is bigger scene on my PC. GPU is in lower performance state(405MHz), GPU usage is only 32% . GPU consumption is 12% of TDP which is around 6W. I have only 11fps, because CPU is the bottleneck(max single thread viewport).
Same scene, GPU in high performance state (1100MHz), GPU usage only 7%, but GPU consumption is 27% of TDP which is around 24W. Same fps, because CPU still bottleneck.
Difference in PC case consumption with my GTX950 is ~20W (66W/85W) which is not much, but try to imagine that I would have bigger GPU beast, then the difference would be bigger. Or another example...with lower performance state you can work longer on notebook when using just battery...also lower heat and noise.