Yes. I get the following error when I set it to False:
File “/home/suncast/venv3/lib/python3.6/site-packages/torch/autograd/init.py”, line 99, in backward
allow_unreachable=True)  # allow_unreachable flag
RuntimeError: has_marked_unused_parameters_ INTERNAL ASSERT FAILED at /pytorch/torch/csrc/distributed/c10d/reducer.cpp:290, please report a bug to PyTorch.