Question regarding --delete-during/after and backup file cases

[Michal Soltys]

A good while ago I asked about difference between --delete-during/delay 
and --delete-after, when per-directory files are updated (all is 
perfectly clear for me here), but during the discussion there was a hint 
made by Wayne, that the outcome can differ in more situations:

" It is useful for things such as --delay-updates --delete-delay (to 
have all updates happen more rapidly at the end), and the option avoids 
an extra dir-scan delete pass in such a case.  And for folks that don't 
have per-dir filter files being updated, it works the same as 
--delete-after (if we disregard certain backup-file cases where the 
suffix is not excluded), just more optimally. "

If I understand it correctly - those "backup-file cases" mean -b option 
and - accidental or deliberate - override of the protect rule added 
implicitly by rsync (as explained in the man page). But if this rule is 
overriden (effectivly allowing deletion of backuped files), then 
assuming no per-dir rules are changed, the outcome will be the same 
regardless if we use --delete-during + --delete-delay or --delete-after.

So there must be something I missed or misunderstood. Could someone 
provide me a simple example of such backup-file case ?