[codesnik]

There're revision control systems based on diffs, but git's power (and durability) is that every commit references only blobs, which are (content addressable) files, not diffs. All the diffs used in git log presentation or git-diff command or git rebase command are computed on the fly from the two stored versions. And yes, if you commit a giant file, and then delete it in next commit it's there forever, until you remove or rewrite a history of a branch that references this file somewhere in history.

There're optimizations on the storage level, compression etc, but on logic level those are transparent