Select changes which you want to commit

When you as developer changes multiple files which belong to different stories, you want to keep changes that belong to the same story in 1 commit.

This gives you the possibility to later on only deploy these changes.

It makes it also better to follow change log.

Solution
Be able to select or deselect the changes you want to commit or don't want to commit.
This is possible in GIT by only staging certain changes to the commit.