Yup. Even if the previous ones haven't been detonated yet. Having a line of ships seeding space behind you with mines is a good way to stop someone outflanking you....
On the other hand, this is only something to do against a fleet without long-ranged guns - if you're going to be under fire as you advance, then either All Power To Engines! (to reduce the time to get into range) or Divert Auxiliary Power to Shields! (to reduce the damage you take doing so) are probably better bets.
Personally, I tend to find that mines are best used aggressively; your patrol, skirmish and raid priority ships are short ranged and quite manouvrable - this tends to result in 'overflying' enemy ships on a regular basis, and dropping a mine out directly on top of a ship that hasn't moved yet (so it will detonate when that ship moves) is quite nasty - especially with a Bimith, who is punting an essentially 'free' 3AD energy mine into the middle of the enemy formation as it passes, which (as an extra bonus) will detonate before the shooting phase, and potentially wipe out even escorting fighters before they can respond.
