What advantages are there in a permanent hair dye?

A permanent hair dye has advantages over the rinses or spray- ins because you don't have to keep applying it everytime you wash your hair. It also gives you much better coverage if grey is your concern. However it will need to be retouched at the roots as your hair grows and it will tend to fade unless you or your hairstylist gives it a "soap cap" occasionally to keep the color even.