Notes are included in the backup for both, but in the client also the client settings. In the server backup but only the info with whom which notebook / note was shared.
In the client backup you have also the settings, templates css files.
You do not need to know anything about databases (backup / restore)
Simple restore and server independent (When you want to cange to a other sync target)
Advantageous if something goes wrong when backing up the server app.
However, some database knowledge is needed for the backup and the restore. Especially if you only want to restore parts of the database.
The backup can only be used in the Joplin server, not on a client for restoring or transferring the data to another sync target.