I don't build trailers for a living or anything but...
Too much tongue weight-
Poor braking/handling from your tow vehicle since your front tires aren't loaded properly.
Poor tire wear on the front trailer axle.
Overloaded front axle and tires. Blowout possible.
Exceeding manufacturer's tongue weight on the hitch, strength issues?
Not enough tongue weight-
Upward pull on the ball and hitch. Not good. You would be relying totally on the lock that slides under the ball to carry the weight.
Rear trailer tire issues.
The boat should be centered over the axles to evenly distribute the weight, erring to the front by a couple hundred pounds from my understanding.