Each time HW: Sanctify and Serenity pops = 60 secs removed from the 12 minute HW: Salvation timer. Without Sanctify & Serenity, taking HW: Salvation as a talent would be useless; it takes too long to reset.
With a near-unlimited resource (mana) with this macro, over-healing is a non-issue: if the boss is dead, everyone is still alive, and you have plenty of mana remaining, then…no one got over-healed.
But I can imagine that having to wait 6+ minutes on an ability that has a 12 minute CD before pull on the final boss would be awkward. Besides…you’ll thank God that you have Serenity and Sanctify in PVP. 
Not sure about why you would mention HW: Chastise; its a damage/stun spell and isnt even in the macro. If you wanted a DPS macro for HPriests, here’s mine:
dCJDcaWsPQERuHTjvQzsIYSvWnvf)sH(MuGDkXEHDtQ9RQ8tPi(TKgOuidLKgSQ0WPsoOuqhJQoNuQwOaTuuPfRKLJYdLk6Pildv9CrnrsKPkYKfW0joTqxMYZOcxNkAJsj2QujBwksBxkPdRYTPsnnLIhROrQu6ZQQgTuLXtIQtkLYzLc11uQoVGEnQyCKWDLIA4rcfpOTnrznwjvcfEKaLUbtlzqoC4D49Eqkzn9CoiO4brUSzBkHc)EdaP2Lkk8GEUjR2LXYXQoJekEKqXdACEz57vHIU53rHh048YY3RFt7(nO4a048YY37UIDqjwuZXepwG2AxaSavSjhSaf0geSaXnQ)9ybQVfY1gSlBibbuFluLz5msO4bnkh73etBUd)E7qx7Dm3n3ra7c0meqCJ6FESaLyrnht4XcuNv3RtqqqKyUAXPEkXQgKklwzrjeKkZEUjRIeeqQ1S8CtwfjiqqHhju8GgNxw(EvOOB(Du4bnoVS89630UFdkoanoVS89URyhKAnlp3KvrccOT2falqfBYblqbTbblqCJ6FpwGsSOMJjESaLyrnht4XcuFlKRnyx2qccO(wOkZYzKqXdAuo2VjM2Ch6A4cngeqKyUAXPEkXQgKklwzrjeuNv3RtqqqQm75MSksqaXnQ)5Xcceqn0P0RYarh7C1lQ8g9ybIT2d0ZPDEdTPfJ1QPLyvJGqGaaa