The Timeless Isle Item, Faintly Glowing Herb, heals 30,000 HP a second when consumed
for 10 seconds.
Splitting up the stacks using shift allows you to take each heal at the same time, making
you virtually indestructible for those ten seconds.
This is of limited use as it can't be taken into instances, but I've found this trick useful
when fighting rares, world bosses and Brawler's Guild opponents, not to mention world
pvp.