Upon detonation, each mine does 1050 points of damage to its intended target as well as an additional 150 points of damage to all other enemy targets within a radius of 1500.
The Advent's mines are powerful defensive tools; if you use them well, you can make a planet a death trap. This type of defense is expensive and slow to build, but these mines are the only mines that follow their target when they pass in close range, and deal the most damage of all mines in the game. Large fleets don't have enough agility to evade all the mines.
Deploying mines around a Transcencia Star Base is a excellent idea, while Destra Crusaders soak up considerable damage. Using the mines to funnel the enemy to a place of your choosing, such as toward a Transcencia Star Base so a Meteor Storm can destroy their fleet, is a great strategy. Mines can also fortify wormholes, especially if supported by Aeria Drone Hosts with fighters that can destroy the Scout Frigates that try to clear the minefield. Mines can also defend neutral extractors, although there would need to be enough mines to keep the enemy at bay while you send a colonizer frigate to capture the extractors.
In most cases it isn't justified to spend resources on mines, but in very specific cases such as those listed above, or when you're in a war where you have to defend a key position, mines can give you a hand in making an overwhelming enemy attack desist, and provide you with time to prepare a counter-attack.