You do not need to be on a 12/12 cycle for an auto to bloom. That is the only advantage of those plants, is that they bloom as a result of the age of the plant, not the light cycle.
I would have to disagree that non-photoperiod flowering is their ONLY advantage.
24/7 for 1 month(most veg from seed for more than a month), and 12-12 for two (if you've got a fast finishing photo strain)
Is the same as 18-6 for 3 months.
Photo strains DO NOT veg, or flower as vigorously as autos.
I haven't seen any photo grows (not from clone) from seed to harvest in 90 days and pull 8 dry zips.
More have been pulled with auto's.
I think auto Mazar was 14 ounces in DWC with LED lights in 80 something days. Single plant.
Think different was like 11-12 ounces with the same type of setup. Single plant.
If there's a photoperiod strain out there that can do that in 90 days max from seed, I'll eat my belt.
I AVERAGE 6 ounces per plant. Some more, some less but I know if I run 12 Think Different plants under 4-600's in a 4x8 tent (ScrOG) I'm getting 5 dry pounds in 90 days from seed.
Some of my logs are on here.