If you try to apply 'Convert to Rectangle' effect, Ai will limit you minimal width/height to 0.01mm — not zero. It means we can't use it to create 'lines'. And this is something appearance and styles will hugely benefit from.

Of course, it should allow to set a reference point too:
https://illustrator.uservoice.com/forums/333657-illustrator-feature-requests/suggestions/32052073-add-reference-point-to-convert-to-shape-effect

And although we have a Transform effect to deal with the angle, having it for the line is obviously needed.