Load entire level at once or by fragments


this is a theoretical question. Say you have a game like super mario. Back then, what they did it in old consoles, or at least for that specific game in the NES, they loaded the level on the fly. It starts with the main “fragment” of the level with the background, sprites, etc…, and they had another fragment of screen. And as long as the player moves forward, new fragments are loaded , and the ones of screen disapear.
Is this still relevan today, or can you just load the enitre level at once without worrying about generating and removing what is offscreen as the player moves around.