If the answer includes "it was been discussed in this thread" then you should just report it instead of replying to it.
The macro should be used while your frost/unholy runes are on cd due to obliterates. For example you could use it after blowing your death runes on an oblit. There should be a point in your rotation where you have 3 oblits in a row using up all your runes at which point you would use the macro combined with a /cancelaura.(assuming GoD) Other opportunities in your rotation are discussed at length in this thread.