Why are vector shapes sometimes left unclosed?

I don't see it often, but I've seen it a few times in vector files: some of the shapes were left unclosed. The SE logo is not an example of this, but I modified it to illustrate my question:

You can see from the outline view that all the shapes are left un-closed. It has no effect on the rendered appearance, but I'm not sure why someone would be inclined to opt for this instead of closing the shapes.

The only reason that comes to mind would be to reduce the file size of the artwork. However, the amount of disk space saved for the example I provided comes out to be a whopping 236 bytes. Is there another reason for this sort of practice?

Answer

I'd say its due to either an inexperienced user leaving paths open, or an automated processes which fails to close paths. There is no technical benefit or reason to leaving filled paths open which I am aware of.

It may seem like a small matter. However, reproduction equipment (imagesetters, platemakers, embroidery, etc) can choke and spit on open vector paths with fills applied to them. Illustrator uses its' own logic to determine how to represent an open path with a fill. But I stress, that's Illustrator's logic and not physics restrictions or "givens". Anything other than Illustrator is free to determine how an open path with a fill should be rendered. And often what is rendered may not be what is expected.

Simply because a fill appears to be acceptable with an open path in Illustrator, you shouldn't assume it's not an issue anywhere else.

The best practice is to always close an Illustrator path if there is a fill applied.

And note, I stated "filled paths". Open paths with strokes are another matter and are generally acceptable anywhere since the path is used as a spine rather than a container.