Git is something that most of us use daily, though there are functions / commands you do not use but still may help in some situations.
You commited something and right after that you saw you forgot to remove log or add another file? Or you just want to extend your message? It is not necessary to revert the commit everytime.
For a long time I didn't know that even writing commit message can have its own "best practices". When I got in touch with git for the first time, this part was described with words like "...and here you can write something short about what's going on in the commit".
You know something worked properly a few days ago and now it is broken? Or maybe there is a new feature and you don’t know when it was added and what was changed? You can use this command and search in history of git. It is easy and fast.