In Windows using Anaconda Python 3.7.1, I had to switch this off in order to get a build. I was getting the following error:
LINK : fatal error LNK1104: cannot open file 'python37.lib'
It relates to this commit:
Merge topic ‘reenable-vtk-python-optional-link’
4c9c2e1a7a Remove the block preventing the use of VTK_PYTHON_OPTIONAL_LINK