IANASubmariner, but my understanding from previous info (and this thread) is that this is a peacetime activity conducted in high-traffic areas, i.e. you wouldn’t be using the scope all too often in wartime (just as active sonar is shunned nowadays unless you know what you’re looking for-- far better to listen than yell).
In peacetime, you don’t want to run a risk of hitting anything on the surface. As long as you’re not in an area near your adversaries, there’s not much harm in watching the periscope for stray Japanese fishing trawlers.