The use-case I was facing at the time of this filing was: creating a "widget" that can be arbitrarily included in any existing web page (drop-in with a script tag) that creates some content, like a twitter widget or something. The widget wants to use jQuery, so it first tests for the prior existence of jQuery on the page. If it finds a jQuery object, it then needs to make sure it's a relatively new (and thus less buggy) version of jQuery. If jQuery is not found, or it's not new enough (at least 1.3), then instead just re-load a new copy of latest jQuery to the page, and then use noConflict() to roll back the page's version to what it was before, and store the new (now sandboxed) updated jQuery just loaded for private use by the widget.
Obviously, the part that's more awkward/difficult is in comparing the jQuery version of any existing found jQuery instance, as it's just a (undocumented) string property, that must be broken down and numerically compared.
If it were an array where the parts were numbers, this comparison would be much easier. But even better, if there was a simple comparison function like "isAtLeastVersion(...)", then the question being asked (is it at least some X.Y version) would be easy to check against.
BTW, there was quite a bit of discussion about this idea on this jQuery github commit awhile back:
Not really sure anything ever came of it though.