Photo 1:
This photo was taken from my wardrobe handles. By right, they ARE parallel, but this was taken in a one point perspective, and the handles seem to meet at a single point.
Same goes for these guitar strings. Weird, right?
This tissue paper box was taken in a two point perspective. Notice how to "corner" of the tissue box is the closest to you.
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The ruler is actually paralell but thanks to 1 point perspectievs, we have this:

But at top view:

Although this marble does not have straight lines i suppose you need construction lines from a two point perspective:(imagine my touchpad's not there, and the background is just blank.

but when at top view it looks boring, right?
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So, in conclusion, I think perspective makes everyday objects look more interesting like the ruler or the handles, and one must master them to have good sketches.