Someone already mentioned it, but I'll reiterate that the Enhanced LRM system came into being during the first panicked days of the Clan Invasion. I'm sure equipping a group of Bombardiers or Archers or Crusaders with a weapon that could (in a pinch) work like a giant SRM seemed like a good idea. Hell it is a good idea. Being able to fire your primary missile banks at a much shorter range is a good thing. But the downsides, especially when Clan tech missile launchers became available, ultimately killed the missile launcher. Better options are available, and they're used.
But at the time, when traditional missile boats were being overrun by fast moving, heavily armed units? Having that smaller minimum range could've been a life saver. (Though why you wouldn't just add SRM racks is something I don't understand.)