I'll never understand why ignorant people make comments without the experience or understanding to justify them. A lot of you have clearly never experimented with it so you shouldn't be contributing. Sorry for being a dick, sitting with my unresponsive brother in the hospital, no patience today...
Anyway...
On most strains 11/13 has a huge effect, especially landrace sativas or landrace sativa hybrids.
I have a Thai plant that goes as long as 16 weeks under 12/12. Attenuating the lighting schedule will see her completely mature in 12 weeks, with fatter buds and tighter growth overall. At 12/12 she doesn't really form buds, more like bracts on a stick.
I do 12/12 through transition (first two weeks, then 11/13 for eight weeks, finishing the last two weeks at 10/14. If you're able to drop humidity and temperature to coincide with lighting changes you will notice even more dramatic finishing expressions.
As for yield decreasing, maybe with some strains, don't notice it with sativas. As for potency decreasing I haven't noticed such, but in the spirit of investigation, I have my Thai plant running at both schedules in different rooms to judge that aspect for certain.
Visual example of the same cut grown under different schedules as detailed above.
12/12
View attachment 666829
View attachment 666834
Harvested at day 84 under 11/13-10/14
View attachment 666830
Bud shots
12/12
View attachment 666837
View attachment 666835
Not 12/12
View attachment 666836