some QT questions

[peckhead]

Some people say to QT all fish. Now i thought i agreed with that but after added a Leopard Wrasse to my qt i dont really agree anymore. Some fish i dont believe should be added such as leopard wrasse or a mandarine.
basically what im wondering is when do you experts think it is a good time to qt and a bad time to qt? do you guys really qt every fish you put in your tank? i used to too but now im second guessing this process.
any insight?

 

[coral keeper]

People say not to QT Mandarin fish because of there special diet. Mandarinfish have a thick coat of slime that ich/ick cant get on. I'm not sure about the Leopard Wrasse tho.