What are "Invisible Columns" and how are they used?
Here's an actual use-case that came up just days after I learned about the invisible columns feature in MariaDB 10.3:

Following a new requirement, I had added a new column in the middle of one of our big tables. (This is accessed by multiple different applications.) While this is the kind of menial task that you wouldn't imagine could result in a problem even in your worst nightmares, this is exactly what happened.

Unbeknownst to me, we had some "innovative" legacy code that was executing SELECT * against that particular table (and several others, it turns out), and then populating a set of variables based on the column names and column order that existed at the time. The end result was that the wrong values were displayed in the user interface, causing much confusion with the users. 

I could have fixed the issue in minutes by making the column "invisible", but since we were still running 10.2 that wasn't an option, so we decided to go the hard route by patching and re-deploying the software. Had we not had access to the source code or for other reasons not been able to modify the code, an upgrade to 10.3 could have been our only option.  

So while this feature is not covered by the SQL Standard, it can nevertheless be useful in some rare cases.