If I recall correctly it damages enemy planets that are direct neighbors to your planet when your planet is destroyed, meaning it gives you an edge at getting revenge by bombing his planet into oblivion. Only really useful if you happen to have a fleet ready there to retaliate (i.e. if you lost the planet due to novalith spam or if you didn't pay proper attention and "accidentaly lost it"). It works similarly to "wail of the sacrificed", with the difference being that the latter can be used intentionally by the player.

This one might need to be rethought or replaced.  It's so incredibly situational I'm not sure I'd bother buying it in most cases.