To give an idea of the vertical field of view benefits of viewport,
here is a giant bat from native resolution (1360) vs 640, 440 and 240.
As you can see the horizontal field of view remains constant, but the vertical viewing space's relative increase makes the vertical view significantly larger!
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Edit: I done messed up the composite image! put the 640 in twice and skipped out the 440, but you get the point! comparing the first (can only see feet) second (can see whole bat) and fourth (can see lots of ceiling and floor) pictures.