I am coming from a P3 Pro and the DJI Assistant wasn't used for that craft. What is the purpose of the DJI Assistant as it relates to the Mavic? Back in the old days, I'd use it to tweak settings on my Naza, but I am not under the impression that you can tweak the Mavic's settings in the same way.

The DJI assistant is for all new DJI aircraft, P4,M600, and now the Mavic.
For the ready to fly aircraft it's not for adjust settings like you used to do with the NAZA. Now all of those settings are in the app.
The Assistant2 is if you want to update the firmware from your computer, download the flight records to your computer, calibrate the vision sensors (not M600), restore to factory settings, or use the simulator.