There are many reasons why you don't want to keep unnecessary feature flags around you.
One way to make sure you do not forget about your old flags is by subscribing to the Stale Feature Flags Report.
This report is an automated email sent to you regulary that warns you about unchanged feature flags.
If you want to get an email like this, just log in to the Dashboard, click your name in the right upper corner and pick Stale Flags Report from the dropdown.
You can decide if you want the report to scan all the feature flags that you have access to, or those only that you have explicitly "watched" by clicking the little eye icon on them.
The report will consider a feature flag stale and include it in the email if its value has not been changed for a certain period of time. Pick your choice in the Criteria section.
Of course, you can set which Environments you are interested in by using the Environment Filter.
By setting the Frequency, you can tell us if you want to get this report Daily, Weekly, or Monthly.