There is two trim envelopes for the aircraft. One airborne and one for takeoff and landing. The takeoff and landing is the most critical.

If the weight is to far forward you will run out of elevator authority in the fare. And if its to far back the plane gets dangerously twitchy in pitch.

The to far rear is the dangerous one because it is when the aircraft becomes unstable and you can't control it. Front heavy the aircraft becomes more stable until you run out of elevator.