The -C/--directory option specifies the root directory of the project that fpm should build/run/etc., so that one can build/run a project without first having to move to it. But if one then wants the working directory to be something other than the root of the project before launching an executable, we currently don’t have an option for that.
For example, fpm run --example -C /path/to/my_project -W /path/to/my_project/example_inputs would, regardless of current working directory, run the example executable for my_project, but before doing so, set the CWD to the example_inputs directory in that project, because presumably the program looks for input files in CWD. I would certainly make use of such a feature in some projects, especially if I could set a default in the fpm.toml file.