It's indeed handy, especially when you have to play brinksmanship on the healing when the damage is coming in hot and fast. (Low-level tank, bad aggro control, non-tanks trying to tank and splitting my casts, confluence of interruption to cast and low hp)
Most normal times that aggro slips (Inadequate tank, No sleeps, overactive healing before hate is built), a whack or two is all a Healer will get in a party with low aggro control. Things have improved beyond the days of "It's ok, i'm not mad.... I always have Reraise on, brb when weakness off"
Every healer at some point will be Tanking, for some reason or another. Be it stupidity, or a product of the circumstances. The Catch 22 is you'll be healing yourself to survive, increasing enmity, and hoping that your team can overcome the hate, without incurring so much damage themselves that the mob is right back on your keester.
Decent armor keeps the damage relatively manageable. Far more so than it was in XI, No Blink to insta-absorb that first hit or two.
If the Tank dies, and control evaporates, we can [Sprint] now for all but 15 seconds of every minute, We can exploit what used to be a [/panic] moment, and kite the Mob right back in a circle into the face of your remaining team.
Old XI people, remember your Kirin fights, hit the mob as he's coming through, or stand in the middle of the circle and hit him constantly. Anticipate, Exploit the mob's forced path until you can peel it off, don't just run behind it feeling useless. /bittervet off.
Synapsis Ataxia 50 WHM~ Ultros
XI From Beta to Sea, Retired. 75 WHM/THF+few other ones I liked playing less...