As for splits in a really warm climate, I'd have to agree with you, why not go right to a medium or deep. But nucs come in handy for so many applications where do you even begin to answer that question.
Now, in a really warm climate when considering nucs for splits, well nucs have less space, so a colony say with a slower ability to build up might do better in a more condensed space, better able to fight off shb/wax moth and as you stated better heat retention.
...JP