I'm taking a look at [the chapter on sprites from a NES programming guide at famicom.party][famicom.party/sprites]. There is a little table which describes what the different sprite attribute flags do:

> | Bit # | Purpose |
> |:------|:-|
> | 7 | Flips sprite vertically (if "1") |
> | 6 | Flips sprite horizontally (if "1") |
> | 5 | Sprite priority (behind background if "1") |
> | 4–2 | Not used |
> | 1–0 | Palette for sprite |

I'm generally amazed by how well the memory space is utilised in the console, so I was surprised to see that there are 3 bits per sprite which are not used. Two of these bits could specify a rotation orientation of the sprite. Why was this not implemented on the hardware?

Were these bits used by game programmers for their own sprite-specific information, potentially unrelated to graphics? Were they left unused intentionally for this reason?

[famicom.party/sprites]: https://famicom.party/book/10-spritegraphics/#sprite-data