About the only thing I've ever used it for was to search out AM NOUOs (which by the way have ceased since 2017), but as of today that access has ended. Fortunately REC has taken it upon itself to step in and retain this information which would otherwise only be accessible through the "black hole" of the national archives.

https://recnet.substack.com/p/fcc-to-retire-cdbs-rec-preserves

FCC to retire CDBS. REC preserves much of its history. Establishes new "Public Access" search tool.

The FCC broadcast filing system used from 1999~2023 may be going away, but it will not be forgotten, thanks to the REC Radio History Project

...The new tool will allow you to access the data that is in CDBS including the recently gathered import letters and public notice comments.

The CDBS Historic View website is a part of the REC Radio History Project and is intended for historical research only. The CDBS Historic View website should not be used to gather information on current facilities.

To access the CDBS Historic View, please go to:
https://cdbs.recnet.com

To review currently authorized and proposed facilities, please go to:
https://FCCdata.org