can it do any harm to use 387.10.10.15.15.108
Define harm. Many people are using this driver. It works and does not break. Added VOLTA support. It does NOT work with the latest CUDA and toolkit properly. The majority of users will never run into those issues, but it does create problems when trying to utilize CUDA rendering on some video applications when used with the latest CUDA driver. Make sure you stick with the CUDA driver(s) and/or toolkit released at the same time as this .108 driver was originally released.
why did NV pull it and strongly recommends not to use it?
A popular conspiracy theory says Apple requested/demanded its removal. The VOLTA support it added may have been part of that reason. We'll never REALLY know the real answers.
NVIDIA's reason for saying not to use is simple - because it is not compatible with the latest CUDA driver and toolkit. Again, use the older CUDA driver(s) released at the time if/when you run into issues and it "shouldn't" become a problem.
Will add - generally speaking, NVIDIA and CUDA on macOS is barely clinging onto life support at this point. If you're looking to holdout for legacy purposes, turn off all updates and just use the stuff as it is. The CPUs in MP5,1 are already EOL'd by Intel. Move to METAL on macOS or switch to another OS platform. CUDA might as well be labeled as EOL'd by NVIDIA for macOS.
If you're on macOS and trying to stay even remotely current, move onto other options (AMD GPUs) and/or at least have a working AMD GPU (certified for the OS) available if you run into issues.
The NVIDIA driver reissues are just for OS build compatibility with OS updates, nothing more, no additional GPU support, no additional functionality, no bug fixes. These OS updates will likely stop around September 2020 if past patterns hold.