Let's say I have a 1GB file on my OneDrive for Business account, and I delete it.
Then on my computer I put back the exact same file on my OneDrive.
Why do I have to re-upload it? You already have the file in the recycle bin! Just hash it locally, and save me from upload another 1GB of data, sometimes with an ADSL connection.
FYI "other services" do it