I use them, especially if I want to neuter a planet to make a safe passage world (nothing worse than a set of mines which destroy my ships' engines when I am trying to pass to some other world) or if I prepare an attack on a powerful tier3/tier4 world. In that case I usually use the combo of siege starships t1 to stir the hornets nest and when some enemies come near the wormhole, Martyrs to tractor beam enemy ships into the world next to the planet I am attacking (planet I am holding and have an army ready to pick them 100 at a time). If mines were present, my Martyrs would have no engines which would end in... well, an explosion.
