Smart files is one of the most awesomest feature in Windows 8. It basically lets you ‘see’ all your files in OneDrive but takes up a ridiculously minute fraction of storage. When you want to work on a file, either through an stop or double clicking, out would auto-magically pull down the whole file. See more here http://gcoupe.wordpress.com/2014/11/13/build-9879-of-windows-10-has-removed-smart-files/
In the latest build of the Windows 10 Tech Preview this feature had been removed. What’s refreshing about the new Microsoft is that we can vote to get it back. Go add your vote here. https://windows.uservoice.com/forums/265757-windows-feature-suggestions/suggestions/6708195-add-an-advanced-option-to-restore-showing-all-oned
You can also enjoy the passionate feedback from users.