It would be nice to see them detonated before they become a threat to the countryside.
Live mines would make harbor raiding less of a farce than in SH3 and SH4, though. Destroyers in shallow water are nasty, of course, but at least you can hear them coming. Having a silent sub-killer, waiting for you to stray in the wrong direction.... Well, that would certainly keep me in the deep, blue water, looking for convoys, instead of slipping into the shallows, aiming for ships at anchor.