There are many people who believe this, and, while it is true for some types of plants, it's simply NOT true for MMJ. Here are a couple of quotes I posted recently when engaged in a similar discussion
"One way in which plants are categorized is by the way they gather and handle carbon dioxide. Cannabis is a C3 plant. It uses the CO2 it gathers during the light period, when it is photosynthesizing. Plants designated C4 also gather CO2 during the dark period for use during the light period. Many C3 plants, including cannabis, do not need a rest period. They continue to photosynthesize as long as they are receiving light.
The plant's photosynthetic rate determines its growth rate because the sugars are used by the plant to build tissue and for energy. Cannabis under continuous light will grow 33% faster than the same plants on an 18-6 light regime." - Ed Rosenthal
"Cannabis is a light demanding plant. Professional growers keep the light on their plants using the 24/0 photoperiod for this reason. Plants that grow under 24/0 flourish and do not need a quantity of darkness in order to rest and perform photosynthesis properly. Plants that are grown in optimal conditions under 24/0 light regime grow vigorusly and the benefits of a 24/0 photoperiod can be seen actively in the results. More nodes are formed, more branches are created, leaf numbers increase, the plant is growing at its finest." - Greg Green
...You getting kick backs from the power companys!?......interesting...I vegged 24/7 when I started, but wasn't really concerned about power usage, cause my lighting was way below recommended levels(and types) and it seemed a lot of peeps were doing it...fast forward a bit...my lighting was improved, but I was worried about cost and red flags, so I went to 18/6...yield was better, but so was lighting and growing knowledge...last couple runs, I've gone with 16/8, again with some personal bests for yield...however...my climate can be unforgiving, when Ya run plants well into October, and may have to run heat to maintain environment...so. it may be worth rethinking...while 33% increase may not be achievable in makeshift home grows, there might be enuff', that makes it worth while...food for thought...thanks Krip......cheerz...h00k...