The "snapshots which are stored as deltas, if that works" part is unrelated to the diffs the git porcelain generates for you when you do a git-diff or git-show.

The "snapshots which are stored as deltas, if that works" part is unrelated to the diffs the git porcelain generates for you when you do a git-diff or git-show. The former is purely an implementation detail of the storage (albeit an important one), while the latter is entirely virtual, calculated from the snapshots every single time you view the data. That's why operations like git-diff and git-blame can take some time on large trees or histories (and why e.g. git-blame has various options to tweak how it tracks files across revisions, because that is not something git does), while git-log is fast.