I think "unused" is probably a better description than ignored.
I've just checked back as far as when that variable was first added (way back in 1.0.0 Alpha) and it has never been used.
With that in mind, there's no expectation for this variable to be used, so at best we would remove it completely, though ultimately it will probably remain and remain unused.
Auto resize will happen automatically, regardless of that variable, if there is a max width/height and the width/height exceeds the max width/height. We also determine whether the server can handle the resize operation by checking the width/height against the config value maxImageResizePixelCount.
If you're trying to do something specific, I recommend posting in the developer discussions forum.