Upvote:2
That page can be used for basically any type of note that the issuing authority wants to record. An incomplete list of examples, not all of which are necessarily applicable to Canadians:
And yes, these are only binding on the originating country: if the passport is endorsed to make it invalid for Liechtenstein, it's unlikely to stop its holder from visiting, but when they return and Immigration finds Liechtenstein stamps, there may be some questions asked. (Partly because Liechtenstein doesn't actually have border controls as such, so you need to go out of your way to get those stamps...)
Of course, in this age of digital records, this all seems a little quaint and these pages will probably go the way of the dodo someday.