I love a big dirty reese bass. The movement caused by the detune is endless. It reminds me of the cloudy rolling effect when you kick up mud underwater. The science behind the sound is neat, too. Best I can summarize my understanding is you have two opposing generators purposely phasing some of each other's voices out.
This explains it pretty well. My anecdotal knowledge says people usually fine detune each saw wave +/- 7 cents from each other, or multiples thereof. https://toolroomacademy.com/features/everything-you-need-to-know-about-the-reese-bass/