There is no doubt that a Star Ship would need a counselor/Psychologist/Psychiatrist on staff, especially on long term missions. In fact, McCoy often acted in this capacity for Kirk, though it wasn't his primary area of expertise. What is laughable and what dates TNG to the 80s is having the ship's counselor seated next to the CO and XO, as if she were of equal importance and was needed on the bridge at all times.
Actually Troi was not on the bridge all the time.
In addition, Troi was not only a counselor, but also emphatic. Perhaps that was more of a reason behind her being on the bridge more than some other everyday starship counselor.