Airlines oversell all the time, so airlines do strive for max load factor (otherwise they don't need to oversell by expecting someone to no show). A profit matrix is usually involved in calculating the optimal fares to sell, so a ticket is available for someone to buy at any given time at a preset price that the airline is willing to sell and fly. If the airline continues to hit 100% in load factor, then a new profit matrix should be generated to maximize profits because the current one is not ideal (whether it's to increase flights, sub in a larger plane, reduce low fare buckets or an overall increase in fare price).

Do remember that when a flight has taken off, every empty seat can no longer generate revenue, hence dead cost (so airlines will typically try to fill the plane as much as possible). This is not like a typical shop where the inventory can be kept for the next sale, airline industry does not work like that.