There is no unjoined form of Arabic. The Arabic script became Arabic when Nabataean script started developing joined letter forms. Unjoined Nabatean is as foreign to Arabic as Phoenician is to Greek.
It does if one is doing typesetting math-heavy documents. Nothing really matches TeX quality or flexibility in math typesetting, not even typst (yet, at least).
In some countries, legal documents are required to not have any paragraph breaks, so you can have a document with one paragraph spanning 100s of pages. OpenOffice has a hard limit of 65534 per paragraph, and it took LibreOffice quite some work to left it: https://bugs.documentfoundation.org/show_bug.cgi?id=30668
The fix looks like a 5 line fix because it is a last step in a very long process of optimizing LibreOffice text layout that started years ago. This 5 line fix could not have been possible 10 years ago simply because the code it is fixing didn't exist back then.