You are a tank. During a tank swap, there is a good chance YOU have an absorb shield from another class or if you have Soul Barrier. Your shield will reapply more frequently than a DPS who would mainly get spot heals.
Huge difference between the neck and a Disc priest. The neck isn't reliable, the priest absorb was. For DPS the neck is complete shit. There has yet to be any incident where the shield saved me from death.