Microsoft's OneDrive cloud storage service is set to receive differential sync later this year in Q2, according to a roadmap from January (spotted by Mary Jo Foley). If you're unfamiliar, the feature would provide the ability to only sync parts of files that have changed, rather than the whole thing.
This would end up saving users quite a bit of bandwidth, especially for those that handle larger files. For example, those that have large databases stored on the service or edit videos should have a much easier time.
In fact, it would save time for users whether the file is downloading or uploading. If you've got a shared file synced to your PC and someone else edits it, OneDrive would only upload a portion of the file from that person's end, and then only download the same portion on your end.
Unfortunately, On-Demand Sync isn't listed on the roadmap right now. This is going to be Microsoft's replacement for the placeholders that were available in Windows 8.1; however, we probably won't see them until at least later this year.