HTMX allows to write less JS and for the most part less frontend code in general. That is the main benefit. HTMX is an escape hatch for backend JS devs too. Please, note that PrimateJS backend code is very compact, which itself allows to write less JS code as well.
With `htmx` template literal tag recently added to PrimateJS, coupling of HTMX and PrimateJS looks much better in the code than previously. Meaning, single JS dev can do a lot even without knowing these two techs deeply, while leaving behind a code that is more likely to be maintainable. Both PrimateJS and HTMX aim to be simple to use and understand for someone being familiar with HTML and JS alone.
The quick start guide on primatejs.com is just an example of how to try PrimateJS quickly.