My idea behind it was for it to be the equivalent of a nuclear submarine, being able to patrol independently for months (or years, since space opera) without the need for a dedicated fuel tender following the fleet around. Besides that, its heavy (though I can't find easy comparisons for most engines), unstealthy, and slowly gets closer to overwhelming the internal shields of the drive and tearing the ship apart from the inside every day.
I have to admit, that's my favorite part.