It's ridicilous how Warlocks always have to cast their spenders, while Shadow Priest / Boomkin / Ele Shaman do not have to cast their spendes.
There is no good reason why Rapture, HoG or Chaosbolt should have cast times. Makes zero sense.
In the case of Destruction this bad design just happens to absolutely fuck you, because the spec doesn't have other instant cast spells, but Aff and Demo do so have some.