On January 18, 2013, Valve decided to make Gearbox's models MANDATORY. The thing is, these models are bugged, and Valve aren't using the fixed ones.

Second, the HD models cause conflicts with mods such as Sweet Half Life, Azure Sheep, and Point of View.

You also can't install custom skin packs. These 2 together remove a big part of Half Life modding history, and let's try to bring the old models back. (and make them optional again)