I guess the funny thing is that each Git commit is internally just a file. Branches and tags are just links to specific commit files and of course commits link to their parents. If a branch gets deleted or jumped back to a previous commit, the orphaned commits are still left in the filesystem. Various Git actions can trigger a garbage collection, but unless you generate huge diffs, they usually stick around for a really long time. Determining if a commit is orphaned is work that Git usually doesn't bother doing. There's also a reflog that can let you recover lost commits if you make a mistake.