The sample chamber helps in sensitive measurements by protecting a sample from external EM fields and ambient light. It also helps keeping optics clean.
In photoelectrochemical measurement where electric currents smaller that 10 nA are to be recorder, the sample chamber forms a Faraday cage and reduces EM noise below pA levels.
Similarly when small light intensity are measured, as with reflected light and an integrating sphere, influence of ambient light would swamp the actual signal.
The connector port on the side of the chamber allows a potentiostat to be mounted directly to the chamber without any cables.Click the picture to enlarge