The 3.3.5 client is a 32-bit application, meaning it can only use up to 2GB or 4GB of RAM. High-res textures can cause "Error #132" (Out of Memory). To fix this, most users apply a Large Address Aware (LAA) or 4GB Patch to the WoW.exe .
Best use cases
The most immediate change is the level of detail. Fingers are separated rather than "mitten-hands," and faces possess actual geometry rather than flat textures. Beyond aesthetics, the HD models introduce "New Player Animations" (NPA). These animations change how a character runs, casts spells, and emotes.
The jump in quality is massive. Original Vanilla and WotLK models typically feature blocky hands (often called "claws") and stiff animations. The HD versions introduce:
Updated looks for iconic mobs, mounts, and bosses.