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If you have hot pixels that either produce maximum pixel values or close to it, dark frames will result in "Measles" on your images as the dark frame subtraction will result in more or less zero values in those pixels, regardless of what actual signal might really be there.
I fiddled for some while with a 350D letting it do in camera darks (Lazy me at the time) and I only ever noticed the issue when I started using my C925 and guiding as well instead of doing widefield images. When dark frames were subtracted either in camera or using properly shot darks turned into a master dark and guiding was introduced the hot pixels would fall in the same place on the image target sub after sub after sub, so the dark frames resulted in any real information in those pixels being lost to the subtraction of the hot pixels.
If you introduce dithering, the hot pixels will be subtracted from different pixels within the target in the light frames so then integration can work better, the zero or low values of the subtracted hot pixels should end up rejected and the true signal will be more dominant.
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