This might be the most specialized off-map artillery in the game. Unlike all other off-map artillery, it cannot be called on any spot you like, but rather, it has to be centered on one of your own points or structures (e.g. a bunker.) To make up for this, it has a very short delay between the smoke warning and the when first shells fall. For a relatively long time, more mortar shells will fall around the point until the ability ends with one very strong circular barrage. Infantry squads that stay under this rain throughout the whole duration will nearly always be completely annihilated. On the other hand, they will be able to retreat with only one or two squad members lost if they retreat as soon as the first shell hits.
Registered Artillery needs a little bit more foresight to use effectively. Most players use it to prevent an enemy squad from capturing an important point - it's particularly useful for defending Victory Points in the late-game. This is a perfectly fine use of it, although you can get the same effect for cheaper via the use of Terror Doctrine's Propaganda War or an Officer's "Force Retreat" ability, to name a few alternatives. On the other hand, Registered Artillery can be used to kill a Jeep or M8 using Raid, unlike the aforementioned abilities.