3.5.1. Possible Paint-Containment Optimizations claims, in point 2, that "unless the clipped content is made accessible via a separate mechanism such as the 'overflow', 'resize', or 'text-overflow' properties the UA can reserve "canvas" space for the box exactly the box’s size."

I can see how resize and overflow might make a larger canvas desirable, but text-overflow is only dealing with how text is chopped off when it extends out of the element.
It does not make the clipped content any more accessible than it would've otherwise been and doesn't imply any ability to bring it into view.

I feel like it should either not be listed here, or there needs to be a better explanation as to why it's relevant.