I really like TM as well, and find it quite useful. It’s like incremental backup on steroids. But I don’t feel it replaces a “snapshot” backup system.
As an aside, I’m surround by people who consider cloud syncing to be a backup, and just yesterday witnessed someone in the grief stage when they deleted a load of photos to save space because they thought they would remain in the cloud. They had even clicked through the “delete delete? Are you sure?”.
It’s almost been enough to get me to have a test LAN and real one so as to maintain household tranquility.
When I worked there, I was surprised to learn that they also often act as mitigation for ransomware attacks (they could roll back your account in time if you contacted CS and explained your situation).
Which is to say, a block-based snapshot is very efficient - your snapshots only take up the space of the blocks that have changed - regardless of which files those blocks make up.
A hard-link based snapshot scheme is also fairly efficient for most use-cases - the snapshot only uses space equal to the files that have changed - even if those files only changed a little bit.
For most use-cases, I find the difference is negligible. However, if you have large files that change by small amounts, a block based scheme (a la zfs) is much more efficient.
Also, at a certain point it just can’t keep up with the changes.