Im on V17. I have gone through many tutorials on follow-ups but I cant wrap my head on how to actually use it. For example

Why is there need for action on this when the closest due date is 17days ago but the follow-up level is 30days

When i switch to 40 days, it says "with overdue" invoices

Or switch the next reminder time it changes to "with overdue invoices"

Im trying to set it up to run automatically but I just dont understand how it works. Here are some of my other observations

• The followup level does not increment(or I dont know how to trigger it). 
• How does it behave when say it reaches 60 days and invoices that old have been paid off. Does the followup level reset itself? If so, to what level? If not, what is the logic there? 

I dont have a question in particular. Any help to understanding how it works is appreciated. Thanks