I don't care about ntcnico's claims, he can defend them himself. But if you cannot see how having capture data outside of the display area could be potentially useful, then I don't know what else to say, apart from "surely the potential advantage is obvious to any experienced engineer." There is no need to give specific examples, use your imagination.
I don't think anyone argues that data outside a window which shows a narrow view of a small part of a signal is not important, and I haven't seen any comment suggesting that.
In fact, the idea that surrounding data is important is the main idea behind deep memory scopes and the standard method of "capture long and zoom in". Because knowing that things outside the original point of interest may turn out very relevant, the reason why we have large memory in mopdern scopes is so we can capture the whole sequence right from the start, and then zoom in to the areas of interest (which there might be many).
So the question is not if data outside the (narrow) window is not important, but why is the scope set in a way that important data is outside the window in the first place.
The idea that one
*needs* this "zoom out" capability one can make-do, under limited conditions, on some scopes, simply because the scope was set to show a very narrow part of the actual signal when one spontaneously decides to that the rest of the signal should be examined, too, suggests to me a lack of preparation. Because especially when you're bug hunting it shouldn't really come to a surprise that parts outside that initial narrow piece of interest will become relevant. Capturing long means having every part of the signal inside view and thereby quickly available for examination in a coherent manner.
And even if you got yourself in a situation where you found your original capture was too short, instead of make-do with "zoom out" it might make a lot more sense to finally set that timebase to capture long so you avoid finding yourself in the same predicament again a few minutes later.
So I fully agree with you, data outside that narrow screen is useful, more often than not. Which raises the question why is important data outside the screen area in the first place. This off-screen data being important is even more reason to make sure right from the start to capture everything in a long acquisition.