In what circumstances would you not "enhance" your class with a "job" role?

[Holyhunter]

its meant for soloing (which there really isn't any solo content in ARR) so that you can cross class more defensive and self healing abilities like Second Wind to more classes

[Crimen]

its meant for soloing (which there really isn't any solo content in ARR) so that you can cross class more defensive and self healing abilities like Second Wind to more classes

Pretty much what he said. It's more for soloing things, but there's rarely any of that going on. There will be few occasions in which the class will be superior to the job in a party.