3.7 Synchronization
You can have a synchronized copy of the contents of your libraries by using OneDrive combined with SharePoint.
If you have OneDrive and are on the computer you want to sync with SharePoint and your files, it’s easy to get started. Touch the library you want to keep up to date locally on the machine. Then press “Yes”.
This function is useful if you need to copy files to a new site, download files for security storage or due to requirements for local storage of files (Please see Microsoft security https://products.office.com/nb-no/business/office-365-trust-center-welcome?omkt=en-US).