Landscape, Night, Portrait, Flower, and other scene modes are great (and vary a lot depending on your camera) when you don’t have the time or interest to fiddle with your exposure settings. They choose the “best” exposure options based on the situation.
For example, Landscape typically chooses a mid-range aperture (11 to 20) because everything is usually about the same distance away, and a safe shutter speed (60 to 125) to make sure there is enough light. For ISO, it assumes there’s sufficient available light, so probably doesn’t have to boost the ISO beyond 100 or 200. Night mode on the other hand, assumes there is very little light, so chooses a high ISO and a safe, possibly slowish, shutter speed, and doesn’t really care about the aperture, so chooses something (4.5 and up) that will produce a “good” exposure.
I must confess that I haven’t used these too much, so I’m probably off the mark on how they work. In any event, I suggest that you use them when you need to, but recognize that they are taking a best guess.