Witchboat --
Think of it this way -- when you trim up, your bow rises and thus you "slap" the waves more making for an uncomfortable BANG, BANG, BANGING ride.
Put the trim down and you have a greater likelihood to "Cut Through" the waves making for a smoother ride.
The larger/heavier the boat the better this system works --- if you have a pontoon boat -- then simply head home
cuz none of this will help.