If done right, playtesting would give player feedback to allow the developers build a better game. Sometimes the feedback could give the designer a change in perspective which can create a more unique experience. Overall, the Game Designer is building the experience for the player, without their input things would be a hit or miss situation.
Importance of Testing EarlyEdit
As the game progresses through production, every change in game design often adds more time and effort. Having playtesting done early on would allow the designer to make the changes to the game with minimal impact on lost work.