The main advantage seems to be no travel the morning of and no need for a hotel for previous night. However, I usually do 6-7am flights and get there before 9a

The main advantage seems to be no travel the morning of and no need for a hotel for previous night. However, I usually do 6-7am flights and get there before 9am, 10am to office after BART from SFO. Flights back go as late as 9pm. In the end, southwest will set you back less than $120 if you book in advance. I also much prefer my own bed, as opposed to hotels or buses, but that's a personal preference.