Even so, with a nonzero highlight ignore setting, you will get some clipped highlights (the percentage you have selected, as area or number of pixels). So it's still a bit different than "No highlight clipping. Full stop.".
In other words, with a reading of 0.0 and SNR limits off, if Highlight ignore is set to 1%, that means 99% of the pixels will be below the target level (Exposure target), and the remaining 1% will be above. If there are no specular highlights, there won't be anything clipped. If you do have specular highlights and their area is smaller than 1% of the total image, they will be clipped, regardless of how bright they are.
With highlight ignore set to 0, and SNR limits still off, any strong specular highlight (or even some hot pixels, if unlucky) will dominate your exposure, even if most of your image ends up black.
This is where the SNR limits come in: if the shadows and/or midtones become too dark, enabling those limits will sacrifice the highlights to protect the shadows.