It just stops the front end lifting so much under power then hitting the ground under hard breaking, which can give you an inconsistent feel to the car.
Restricting front droop also reduces on power steering making the car want to straighten up under power, again making it easier to drive. (A car with slight understeer is easier to drive than a car with oversteer).
Outdoors you maybe want a little more droop than indoors, but this all depends on how bumpy the track is. The car with no limiters in the front shocks has more than enough travel for any outdoor track in my opinion.
Craig Collinson