It’s not a technical question, more a process question.
Let’s imagine a customer is creating a ticket asking for sales information. You answer it, but then the customer isn’t answering right after, and tell you he’s busy with something else at the moment.
So you need to have a list of customers to reach again after a bit to get their status. How do you deal with this? Do you let the ticket opened? (so it’s a lot of ticket opened, right?). Do you close it? (but then, how to be sure to find back this customer when you want to come back to him?)
Or maybe you put a special tag and you create an automated rule based on that?
The pending reminder state is ideal for that case.
Zammad by default has an overview called pending reached which will display all affected tickets that reached their reminder time. Also, if the customer answers (no matter if before or after the specified time) the state will automatically switch back to open.