Airport Time Capsule permanently deletes any information because it’s either full?
Probably best to clarify things here.
Time Capsule is a wireless router with a built in hard drive.
Time Machine is software on your Mac that backs up data from your Mac and stores that data in Time Machine backups on the Time Capsule.
Time Machine backs up the changes on your Mac. If you delete a file from the Mac, Time Machine will at some point delete the file from the backups on the Time Capsule hard drive.
Normally, the file will be deleted when Time Machine senses that the drive is starting to fill up and it starts looking for ways to create more space for new backups.
But, I have seen instances during testing where the deleted file on the Mac is also deleted quickly from the Time Machine backups on the Time Capsule.....within the next few days or so.....even though there is plenty of free space available on the Time Capsule.
I thought the Airport Time Capsule could be used as any regular external hard drive?
It can, but the primary use for the Time Capsule is to store Time Machine backups. If you decide to store regular files on the Time Capsule......You have no fallback if the file is damaged or becomes corrupted, or as I said previously.....when....not if....the Time Capsule has a problem.
Only the most foolhardy of users would keep important data on the Time Capsule.....and not have another copy of that important data on another hard drive.
When your Mac fails......you have your Time Machine backups on the Time Capsule.
When the Time Capsule fails....you still have your data on the Mac.....unless you deleted it from the Mac.