http://isdb4l77sjqoy2qq7ipum6x3at6hyn3jmxfx4zdhc72ufbmuq4ilwkqd.onion/docs/guide/making-connections.html
It means that removing this address will not break the contacts made via it (like changing an email address would), it would only prevent new connections, which makes it a good solution against spam and abuse. Vulnerability to attacks Until the connection is established, anybody who intercepts this link can connect to it, so it has to be verified with the original contact that the connection succeeded.