These are also censorship resistne checkpoints over #nostr because they contain the block hash. Important because:

"The solution we propose begins with a timestamp server. A timestamp server works by taking a hash of a block of items to be timestamped and widely publishing the hash, such as in a newspaper or Usenet post [2-5]. The timestamp proves that the data must have existed at the time, obviously, in order to get into the hash."

- Satoshi Nakamoto, Bitcoin White paper