For quite a while, I've have had a shell fcn that will take all the untracked files listed in a git status, and push them to .git/info/exclude. Generally applied after an add+commit of everything I do want to go generally into the repo.
Usually when I'm working in one part of the codebase and I have sample data or something at a specific path on my local machine and Im testing the same thing over and over again will I make a Makefile or something and info/exclude it to help me keep focused. That's one way I use it.