Why?

Fundamentally, there are two different backup approaches.

Timed snapshots - Protect you when you forget to make checkpoints as you work towards step 1.
On demand snapshots - Capture things like when you finish an important edit and everything is working in step 1 of your project.

Each serves different purposes. Neither is a replacement for the other. You should probably be using both.

The author has used both types, and developed AnnotatedBackups because he prefers on-demand backups for development work.

On demand backups are stateful. In other words, they represent a given moment in time selected by the developer.
- Often that moment is when either something is now working, like a button on a form. :-)
- But it might also be when something has just gotten messed up. :-(
  
  Saving things in the broken state might help recover some of what would otherwise get lost, before the now corrupted project is closed and recovery begins from an earlier backup.
On demand backups can hold a comment to say how things were when the backup was made. So a month from now if you're looking for when something mysteriously got broken, it is easier to sift through your many backups with some intelligence, other than just date and time.
- So for example, if you have to save a system that is bad, you can note down what the nature of the trouble is. You can't do that with timed backups.

BTW, if you're looking for a timed backup option, like to protect casual users who aren't interested in development, here are two places to look:

LibreOffice has a built in timed snapshot feature; see Tools Options... Load/Save General Save Save AutoRecovery information every N minutes.
And check out this add on.

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