I'm not thin and so long hair emphasizes my weight and generally makes me look sloppy. I think hair smells after 3 days of not being cleaned. It's like a big air filter, it catches dust, germs and odors plus neck and scalp perspiration.
I use no soap shampoo and that makes my hair shinny and gives it a lot of body. The best place to buy 100% no soap shampoo is at a dog salon! The high dollar show breeds can't tolerate soap on their skin.