According to the output of git help clone the --local option does the following:
--local, -l
When the repository to clone from is on a local machine, this flag bypasses the normal "Git
aware" transport mechanism and clones the repository by making a copy of HEAD and everything
under objects and refs directories. The files under .git/objects/ directory are hardlinked to
save space when possible.
If the repository is specified as a local path (e.g., /path/to/repo), this is the default, and
--local is essentially a no-op. If the repository is specified as a URL, then this flag is
ignored (and we never use the local optimizations). Specifying --no-local will override the
default when /path/to/repo is given, using the regular Git transport instead.
If I'm reading this correctly, the second paragraph says this option will default to on whenever a local path is given, and will be ignored whenever the given path is not local. So what's the point? How can it even ever have any effect? Is it basically a no-op stub for compatibility with older versions of git when it did something?