Checkout is important when libraries get busy.
When you and your coworkers get used to working with your SharePoint library, it will turn into a thriving hub of activity. People will be opening and editing files all the time! As a result, things may get confusing if several people try to edit a single file at the same time.
You can always click the file name and choose Edit, as explained in the course, SharePoint document libraries I: Introduction to sharing files. But in busy situations like these, if you need to work on a file for more than 15 minutes, we recommend that you check out the file beforehand. This will reserve it for your use so that others cannot change it while you are working on it.
There are other benefits, which this course will explain.
Click Next to learn all about checkout.