Does the version of OneDrive that works with SharePoint Online alter the sizes of the files that it synchronizes?
Here's what I'm seeing...
1) I've set up an initial SharePoint Online site for one of my agency's departments. 2) Rather than sync this department's original file directory on the local server, I made a copy of it, then synchronized that copy with the document library up in SharePoint Online. 3) I then used a file compare utility that I have relied upon for years - FolderMatch - to compare the original folder with the copied/synchronized folder.
To my surprise, the size of many, many files had changed! As far as I can tell at this point, the files whose sizes have changed are all MS Office files; e.g. Excel, Word, etc. PDF and text files seem to have retained their original sizes.
NOTE that if I go into OneDrive/Manage Storage, at the bottom of the Site Settings/Storage Metrics page I see the comment "Total size includes any versions and metadata associated with the file". So is difference in file sizes due to OneDrive adjustments in the file metadata?
It depends on files, the big difference in OneDrive and SharePoint is metadata, you may have many metadata columns in a file that when you are moving them to the OneDrive is automatically being deleted. I think to find the reason you need to compare the same file in the Local Server\OneDrive\SharePoint and give us the numbers.