So I get sticking your camera right up in someone's face looks weird because too close so generally people want 85mm-200mm for head shots. but beyond that, if you are taking nonhead shot portraits, what do the focal lengths do? is it just a matter of you choose closer to 35-50mm if you want the background around the subject and you chose like 105-135mm to use the compression to isolate the subject from the context of the background and the only other big consideration would be how much physical room you have to shoot?
IE if you are shooting at a park and have room and want the background to fuck off, the compression of 135 mm or 200 mm will do that the best, where as in a studio with a controlled background you might pick 50mm or 85mm because lol no space to get the 2/3rds or what ever % of the body in shot you want?
Let's say I want to do cowboy (mid thigh up) framing, 40mm, 50mm, 90mm and 150mm would all work fine and it would just be a matter of how much physical space I have and how much I want to show the background vs use compression to isolate the subject from the background?