Nicholas Guriev [off-list ref] writes:
It allows for uniformity with the --untracked-files option. Also
the new short flag saves the number of keys to press for the
typically git-status command.
Unlike "-u', "-i" is supported by "git commit" which shares the
underlying implementation, and that is the historical reason why we
never had "-i" shorthand, I think.
While I do understand why sometimes "-u" is useful, especially
"-uno", to help those whose .gitignore is not managed as well as it
should be, I am not sure why a "typical git-status" invocation would
ask for "--ignored" that often to require such a short-hand.