This is useful so you don't riposte damage to your target and you can control how fast you kill something. We used to just fishing pole for this, but the cone of the mystic has some stats. Truth be told, anytime this is necessary, the stats on the Cone are going to be irrelevant, might as well just be using the fishing pole - but it's something cool anyway.
This can be helpful if you are PL'ing a lower level character such as gathering up a large train of targets with an SK then the character getting PL'd can do slight damage to each mob before the SK applies a damage shield to cause the mobs to die. The lowbie gets all the xp this way for deep red con targets.
Also useful if your high level doing lower level raids/content and you don't want to kill a target faster than an event timer needs to run - doing so can cause events to get buggy.