‘Delta sync’ or ‘differential sync’ is a system where each time you make a tiny change to a 2GB file you don’t have to reupload the whole thing. Over and over again. Only the changed bits get uploaded. This speeds up large files with small changes considerably. We're talking like 3 seconds vs 3 minutes for large files! If you work with certain types of files (e.g. large, text/XML based files with small changes), this is absolutely essential.
However, most cloud sync solution don't offer it. For example, Google Drive and OneDrive don’t. One of the only cloud sync solutions that does have it is Dropbox. Their recent (completely pointless) overhaul of the UI notwithstanding, Dropbox is still unbeatable if you want all your work files synced between multiple locations and need a good delta/differential sync system.
External links
- Myths and Facts about Delta Sync – Why Delta Sync doesn’t matter? (I disagree: it does matter)
- What is an incremental backup? (on experience.dropbox.com)