These ppl usually ignore the part that I turned off Cleric Stance and cure. there is no delay between switching off -> regen -> switching on. (it's also very annoying, lots time I press too quick so finally waited 2.5 sec Cleric Stance turned off, but then instantly on again...) Well, in consider many WHM don't even know you can switching between stands very quick (at CT atomos boss for example, many WHMs in pt usually asked me as whm "do you want to cure or attack?" Even in one case, the person told me I can't do both...I just told the person "watch and learn" :P)
situation 2: Holy and Stoneskin combo. I use that a lot during High/Elite dungeons. Within like 4-6 mobs, a geared tank can survived with this:
Divine Seal -> Medica II -> regen (these 2 combine give the person 800-1100 hp per tick) -> stoneskin (due to your initial one already broken) -> regen -> cleric stance -> holy -> stoneskin -> holy -> stoneskin
stoneskin can usually last at least one GCD time with 3 mobs on tank. 2 mobs on tank, you have ~ 2x GCD time. single mob on tank you have ~3x GCD time. so knowing this, you can just stoneskin -> holy -> stoneskin -> holy ... with 2 mobs on tank, you can stoneskin -> stone II -> stone II -> stoneskin while tank is losing little hp.
for the CT atomos,
let me just muttering little more, you can stoneskin -> regen -> cleric stance -> stone II ->stone II -> stone II -> (here the mob is almost dead with other DD's help) -> stoneskin (end of here usually the tank is about to take off for next mob) -> cleric stance (off) -> regen (before tank is out of range) cleric stance (on) -> stone II x 3
in normal cases, my cleric stance off time is ~ 1 sec. so some ppl might missed it and say "oh why you use regen while cleric stance on" but you know, still, in most cases that healer sux.
situation 3: Rushing. If whm has confidence that mobs will die before tank, I think it's ok.
like that 9 gobs place between 1st and 2nd boss of Brayflox's Longstop (HM), I once saw one whm (I was drg) ran in with Cleric Stance. WHM just open Presence of Mind and nuked the hell out of gobs. all gobs died before tank with a single Benediction in between. But, then you can see some are lazy but tank is dying, so I think during this time throw a cure or two under Cleric Stance is still fine.