My main use case is upgrading codebases that depend on ffmpeg. I work for a shop that does a lot of media encoding and analysis across several independent systems, and we can’t upgrade all of them at once when a new ffmpeg is released, which means that for a while we’re actively supporting versions N and N+1. With this plugin, each codebase can declare which version of ffmpeg it wants in .tool-versions, and I don’t have to remember to do the uninstall/reinstall dance.
Most people won’t need this, but a few might find it very helpful.