The name of the preference "Enable no-recompress rendering", along with the content of the Help file, imply that no-recompress rendering will disabled if the preference is unchecked.
However it only applies (buggily) to long-GOP formats such as MPEG-2. Intra-frame formats such as DV, XAVC-Intra & MagicYUV have never been affected by this preference; they smart-render anyway (tested back to VP10).
It's not a major issue, as most users would just want to enable no-recompress rendering for as many formats as possible, but it threw me when I was trying and failing to force recompression of a MagicYUV clip to test the lossiness of its different varieties.
Before Vegas Pro 13, this preference used to be called "Enable no-recompress long-GOP rendering". No idea why it would be changed. I suggest it should be changed back to that and the Help file should be clarified. Alternatively it could be made to truly apply to all the listed formats, or it could be enabled by default and hidden in the internal preferences.