At this moment I can see there are over 1.3 million "*.done" files at pg_xlog/archive_status folder.
The first ones are there since 2013.
As you may suppose this server has been rebooted several times since then. And daily backups are generated.
Is it safe to remove the old ones manually without exposing data lost?
What about to hold only last month ones?
I think so but it would be better to have your approval.