Red dots usually have less parallax error because the dot images are projected onto the reflective front lenses and will track toward the bullet impact changes when viewed off center by the shooter.
Regular reticle scopes have fixed hairs that cannot offset for shooter alignment errors and therefore require a straight through viewing, otherwise bullet impacts can be off aim.
Pistol shooting is less felixible in eye-to-scope alignment and parallax errors can be frequent with a traditional scope.
Rifle shooting requires the shooter to place his cheek onto the rear stock and therefore allows for a more consistent fixed aiming position and better eye-to-scope alignment, thereby reducing parallax error.