It won't hurt your CPU at all.
- If the framerate is uncapped (V-Sync off etc.) ideally your GPU would be at 100% utilization at all times. If it's not, it means that something else in your system is holding it back - typically the CPU.
- If the CPU is at 100% and the GPU is at less than 100% utilization, you would need a faster CPU to improve the framerate.
- But if the CPU and GPU utilization are both low, it indicates an optimization issue with the game (though any of the above could also be optimization issues).
Here's an example from
Vampyr:
GPU utilization is only at 65%, overall CPU utilization is at 17%, and the framerate is only 47 FPS.
If the GPU could be fully utilized, the framerate should be ~72 FPS rather than 47 FPS.
When looking at per-core CPU utilization, we can see that many cores are sitting idle, many are at only 15%, three are around 30%, and one core is at 85% utilization.
So the game is barely using more than 4 cores out of the 16 available, and most of the workload is being placed on a single thread.
Though that thread is not at 100% utilization, it's clearly the bottleneck here. If the game was better multi-threaded, it should be able to better utilize the GPU.
I could upgrade this system from a GTX 1070 to a 1080 Ti or Titan V, and performance would still be stuck at 47 FPS.
The only things that would help are either upgrading the CPU to something which has better single-threaded performance, or if the developers were to patch it to spread the work that is being placed on a single core across multiple cores.