In my case, I have an IT Team SharePoint site which holds all of our IT documents. It makes sense to keep all our IT documents together. For the most part, the site doesn't need to be synched anywhere because it's mostly a storage mechanism. For example, our Finance and Invoices sub-folder is a place where we save invoices. It's not a place where we go to edit them.
One area that I do need to be able to synch however is our projects and strategy area. Our projects are always needing updates and modern day IT strategy needs to be increasingly agile. It's always in a state of change.
Step 1: Add a New Document Library
Start by clicking the cog in the upper right corner of SharePoint and choose Add an App.
The app you want to add is called Document Library, so choose this, type a name for it, in this case Projects and Strategy and then click Create.
Step 2: Move the Files
Next, you need to navigate back to your existing documents and enter the existing Projects and Strategy folder. Click on the circle near the top to highlight all of the documents in this library.
With all of the files and folders highlighted, click Copy To. You can't move files into different document libraries, you have to copy and delete instead. Given that SharePoint sometimes doesn't copy things correctly, this isn't such a bad choice.
The Copy To command will present you with some choices on the right hand side which allows you to choose other SharePoint sites and libraries. Navigate to the newly created library and choose copy.
When the process is over, check that the files were correctly copied and then delete the folder out of the original area. Note that if you shared the files with anyone, you'll need to reshare them from the new location.
Step 3: Make it Easier to Locate
If you're using Office 365 apps, your new library should already be fairly easy to locate but if you want to make it easier for casual browsers to find files via your SharePoint site, you'll want to add it to the menu.
Click on the HOME menu on your SharePoint site and then scroll down to find recent activity. You should see your new library. Click on your library and copy the URL in the browser's address bar. This should be the most direct link to your library.
Next click EDIT at the bottom of the left hand side navigator menu.
This puts the navigator menu into edit mode. Move your mouse to an area between entries and you should see a plus (+) sign. Click on the plus to add a navigator entry. Don't worry if it ends up in the wrong place, you can drag it around later.
Paste the URL address that you copied as the address and type your document library's name (or a shortened version of it) as the display name. Click OK to accept the changes.
Your new navigator link will be added. You'll also find that if you click on the three dots on the menu, you can indent it. This is a good way to keep your document libraries together. Click Save to save the navigator arrangement.
Synching is now Possible
Now that your document library is smaller, you should find that you can Sync your new library.