Blast finishers can be used to stack group buffs on certain Combo Fields. The most common applications are Might-stacking using blast finishers inside a Fire Field (3 stacks for 20 seconds) and Stealth-stacking inside a Smoke Field (3 seconds).
The Elementalist trait Persisting Flames also makes them grant Fury with each blast finisher, which can be shared by the Chronomancer using Signet of Inspiration. Due to this, skills like "For Great Justice!" or Furious Pounce (Tiger pet) are usually redundant in fractals.
Below is a list of frequently used blast finishers among all professions. Note that it is often required to swap to different weapons, make sure to swap back before you enter combat.