Why OneDrive has to synchronise all my folders and files each time I upgrade?

[lawalhu]

When I upgraded to Windows 8, OneDrive hand to synchronize all my files, a process that consumed alot of internet. It was like I was uploading those files again, even though they were already on the OneDrive server. I experienced the same thing when i upgraded to 8.1 and when I tried a Windows 10 tech preview. And now my files have to be synchronised again for installing windows 10. It's not the same case with Dropbox, which only index files without consuming much data. Is that normal with OneDrive or am I doing anything wrong?