What does AstDB actually do?

So I’m reading this page: https://wiki.asterisk.org/wiki/display/AST/Asterisk+Internal+Database

One of the functionalities is:

Asterisk uses it to store information that needs to persist between reloads/restarts. >Various modules use it for this purpose automatically.

What are some examples of these modules? If I just make two extensions that need to talk to each other internally, is the database used in any way at all?

If you register a SIP device to Asterisk, then AstDB is used to persist the information across restarts so that if Asterisk is restarted you can still call registered devices. That’s the major one. It can also store custom device state information, and any arbitrary information that someone decides to store in it for usage in the dialplan.