When you want to do nonstandard things with logging especially for debugging and monitoring I recommend
to add an external syslog server. Of course logging over the network means you won’t get logs about network
disconnections that would be forwarded over that same connection, and you also miss some of the startup
messages that are sent before the network comes up, but on the other hand you can select the syslog software
that you want and have the features that you like (including storing all logs in a searchable “database” more
powerful than you can ever imagine).
This way, the built-in logging system can be kept simple. I usually don’t even log to disk, only to memory.
W.r.t. clearing the log: sometimes one can get out of sync when typing usernames and passwords, especially
when using different systems where sometimes the username is already specified in the (ssh or ftp) command
and sometimes it isn’t.
When you accidentally enter the password where it asks for the username, it is logged and kept in a place where
you cannot easily delete it.
There should be an option to never log usernames on failed logon attempts. And maybe it should be
possible to overwrite them in the memory and disk logs.