You save a 200 MB file. One word changed. Re-uploading 200 MB to sync that change is absurd. Delta sync is how you avoid it. The Core Idea Split the file into blocks. On an update, compare the new version’s blocks against the stored version’s blocks. Transfer only the blocks that changed. Rsync pioneered this. It computes a fast rolling checksum for each block on the remote side, sends those checksums to the client, the client finds which local blocks match and which don’t, and transmits only the mismatches.