Advantages: It can operate from a variety of operational distances (although it's less common for these types to be used at long range). It's easy to mount and adjust, since the transmitter and receiver are housed in the same module. Disadvantages: The reliability of readings can be more easily impacted by the objects shape, colour, material, and distance, as well as by various other environmental conditions ? for the above reasons, to reliably detect and object it must be able to bounce a reasonable amount of light back at the photosensor.