Allowed for Itemid override with url/?Itemid=

I just noticed this in the Changelog of release 2.2.3What does it mean?
Is it a new feature or is it related to the inner workings of SEF Advance?
???

It's intended for extension developers who need to be able to quickly provide different Itemid than the one that SEF Advance internally calculates.

For example, a component could have several menu entries with different settings. With non-SEF URL there would be &Itemid=X in URL and that's how different settings are accessed. However, SEF Advance will have a unique URL and thus only one Itemid. Now it's possible to force a specific Itemid by appending this query string to the URL.

Of course, it's not really best way to do this because you will end up with not so nice URLs. A better way to address this issue is to use SEF Advance extension (sef_ext.php) where you can specifically assign an Itemid internally.