The fan leaves do not need extra sugar during veg. If you want to give your plants more carbs during flowering, there are products for that that are put into the water.
It's just one of those old wives tales,not to be taken seriously.It does nothing.
A comment like that really doesn't need all these postings unless you are really that gullible.
I just write it off as a beginner doing something he/she heard about but has no idea what they are doing.I know I've tried some silly things when growing,when I didn't know any better.
So it's silly and doesn't work.
The End!