It can be a very, very,very heated topic either way.
Myself having read numerous threads about it and many first hand experiances I think it comes down to 2 things.
1. Indoors it can be asset since growing indoors is not a natural method by any means due to using a lite source to dictate spectrum and intensity VS the sun. Not saying it cannot help outdoors but really seems to be used indoors more. If your trying to flatten a plant out and control stretch it is a benifit. It is no secret if you go into flower you can pull the all the fans off and stunt a plant and avoid stretch. I have done this many times to avoid stretch all together of the branches and vertical growth. Its really about how you are wanting to manipulate plant growth. The only way I would intentionally stunt growth from stretch is IF I have clones I have taken from a plant right after it has went through stretch and reveg the clones. Yes it is not a fast method it will take atleast 1 or 2 flowering cycles to have a clone I can work with.
2. It is going to be strain specific AND also it is just a method to assist your way of growing.
I have tried this over the years through various growing methods. Does it work every time? No. If the plant is a strain that responds to this in a good way you will gain in yeild but it is mainly due to the fact you have less popcorn and larf lower down in the plants structure. The larf and popcorn issue some use lollipop to deal with this instead or double stack bulbs. The best reults I seen is when I am growing vertical or on a screen flat because I am heavly manipulating structure.
Some strains the really leafy types seem to benifit from it from what I have seen.
Really all I can say is this. If you want to try it then start out in veg and continue on into flower. Until you try it out yourself you just will not know. Only remove fans do not remove leaves from the budsites unless they are shading other bud sites dramacticlly.
If your going for a main cola type of grow it may not be much benifit unless your in the final week then I remove leaves so its easier to trim fans and bud site leaves since the plant is on its death bed. If your after and willing to spend the time in veg to promote lateral growth for more bud sites this maybe a method that may help. For me it really comes down to structure of the plant. I want to encourage as many bud sites as I can get VS trying to have 1,4 or 8, or 16 main colas.
I am 1 that believes that fans indoors are really not needed since the fans do store sugars ect. That can be very usefull outdoors but indoors since I feed constantly I am not relying on the fan leaves to store what the plant needs for a later time to be used. Fans do have a lifespan, by no means am I saying as soon as a fan grows back remove it immediately. IF I defoliate I start in veg, wait until I know stretch is over with day 20 roughly then every 10 day ish from there on out. It is very strain dependant and very dependant on how you are growing your plants. Its not a method for those starting out, YOU HAVE TO KNOW THE STRAIN VERY INDEPTH to have this as a advantage to your grow.
You can look at grapes, fruit orchards, tomoatoes ect honest very documented Ag science and for some instances it is a benifit not a hinderance. You just need to apply the method to your situation and see how it comes out. There is factual honest science behind it.
Strictly my opinion, miliage may vary. By no means am I going to get into a pissing match with anyone that does not agree with me, so know this now I have used it, I still use. I don't care what others that do not use it have to say. My feelings mean nothing, I utilize science and plant repsonse to tell me either way. Plant respone is mainly what I go by, and that is why this is NOT a begginers method.
It works for my garden, my way of manipulating the structure I want for me nobody else. Not be a snob but just not going to argue it with anyone there is no need to argue anything because its not changing my mind at all in any way. I use it as I see it is needed. It is just a method.....