Lol when you tuck, basically it would be somewhat same as cutting as ur leave surface won't be getting much light(if don't believe, get a light sensor and test, smallest angle to a leaf will change the amount of light received drastically). Last few days of flower I don't mind cutting some fan leaves, especially if overcrowded. Obviously you won't cut fan leaves with bunch of trichomes but the more yellow ones which some tent to be at that stage. Have u tried doing so? If not try before talking so certainly. Nothing is 100% right or wrong and will only depend on circumstances, sometimes folks cut branches and large fan leaves simply for better air circulation, again you don't practice that every time but saying NEVER do it could very much be misleading, peace.