Increasing the seat angle (moving the saddle forward) tends to improve power and, by allowing a flat back, aerodynamics.
Opens the angle between thighs and torso which can improve breathing and, significantly for triathletes, reduce the amount of straightening required when starting to run.
With tri-bars the disadvantages are handling, balance, control, stability, poor forward vision and climbing.
Without tri-bars there is also too much weight on the hands, arms and shoulders for sustained effort.