... that said, before Mimic brought us the central config db, maintaining <clustername>.conf across clusters was a pain. When testing or troubleshooting one would need to persist changes across all nodes, and in the heat of an escalation it was all too easy to forget to persist changes. Even with the file templated in automation, consider what happens when an important change happens while one or more nodes is down ... then it comes back up.
No doubt but my question is what happens if I put the ceph.conf, can be any unexpected side effect.
ceph.conf keeps data in sections, so all the global stuff gets read by all daemons and clients, then you can have OSD specifics and down to instance-specific data for osd.123 in a section of its own if need be, so it is certainly made so one file could work for all of the parts of a ceph cluster. But as said, now with the ceph config db, you only need a super short conf with the ips of the mons and possibly the fsid and it will pick up the rest from the config db itself. -- May the most significant bit of your life be positive.