Another use case for the app I am developing! The basic idea: You can enter an item (i.e. "MyOwnShop Cert") into the list. From that time on, it will be tracked how much time passed since the item was entered or renewed (by clicking the renew button). The item with the longest time since entering/renewing is at the top of the list.
Compared to schedules and reminders it has the advantage that the item is not out of our mind once the reminder or schedule pasts. It just sits there dutifully and its timer keeps increasing.
I use it for keeping up with middle-term contacts ("Wow, I have not written Carl for 3 weeks?") and health-related issues. Logging in stuff that easily spoils would be another use case. And, apparently, cert renewals :)
We issue certificates automatically if none is existing when connecting to a website and renew the certificates in batches 30 days before they expire. When renewing, we merge certificates/hostnames into bigger certificates with 90 hostnames so we don't have so many moving parts.
If renewal would break, however (as it did once or twice before), nothing bad would happen because on page load there would be a new certificate issued.
I used manual renewal for LetsEncrypt for about 4 websites on other shared hosts & renewing them every 3 months was a pain; had to keep reminders and schedules just not to miss renewals until I synchronised their renewal schedules to batch (manual) renewing them.
I had automated renewal for 1 website on a cloud server, it was a one time effort, I never had to bother about SSL cert for that site and the most favourable of them all.