In US boats this was widely used in addition to regular lookouts. Basically, the persicope, fully raised on the surface, and in high power, gave a higher, farther, and better view of the horizon, and was used to find ships.

You needed the constant survelliance and quick reactions of multiple live lookouts to watch for airplanes. Also in surface action (sually at night) human lookouts were necessary to give constant all around coverage to avoid a surprise by a escort, or ramming, at least till radar became widely used. So the persicope watch was used in addition to live lookouts. Only in severe weather, or sometimes in surface combat when a commander might want to save the time of getting lookouts below in case he had to submerge, were lookouts not present on a surfaced sub.

I don't know if the Germans used this kind of periscope watch. If it made sense for a given situation, I would suppose so, but I don't know.