What 'bad things' can happen if you edit skyrim.ini to register the hi-res DLC texture archives...
sResourceArchiveList=Skyrim - Misc.bsa, Skyrim - Shaders.bsa, Skyrim - Textures.bsa, HighResTexturePack01.bsa, HighResTexturePack02.bsa, Skyrim - Interface.bsa, Skyrim - Animations.bsa, Skyrim - Meshes.bsa, Skyrim - Sounds.bsa
...-and- also used the esp's for them (in fact, used the 3 esp's for the 'new' hi-res DLCs, but did not add HighResTexturePack03.bsa to the list of registered archives).
Obviously, you shouldn't do both, and using the esp's instead of editing the ini is (apparently) the better method now with the 'new' hi-res DLC. But, just for the sake of science, the accumulation of knowledge, or whatever, what might happen if you do both?