It seems like it might have some effect on enemy movement (since SMW enemies get activated shortly before they get scrolled into view). Nothing stood out as odd in the sample video (aside, perhaps, from the appearance of mole mounds being more jarring than before, since they still required the same proximity before they start appearing), but I wonder if the wide view creates some odd timing at some points later, e.g. if some spike columns slam earlier than they otherwise would.
Or were those enemies, as viewed in the video activated at that distance even in the original game, well off screen (and therefore the tweak is purely visual)? In the original game, there certainly was some activation area beyond the viewable 4:3 screen -- I recall that Chucks would throw balls well before they were themselves scrolled into view.
I imagine certain secret spaces may be more obvious, at any rate.