Spot laser have two kind of spot characteristics, one is circular, and one is like a small line. Depending on the application one is better than the other.
Contact sensors need to have physical contact with the object. The pin inside the sensor are addressed so even if you lose power and move the sensor, the new position will be present when power is back. High accuracy for small difference in height.
A scanning laser micrometer uses a rotating optical element to reflect or refract a laser beam through a measurement area and across the path of an object to measure.
Profile laser project a larger line on the object so we can create a profile image. These systems are also supporting encoder so then we can create 3D image. With these data we can measure on different target and are not in need of external light