Common mistakes when using collision prefabs in 3D models include mismatched shapes, overly complex geometry, and ignoring scale or layer settings. - **Mismatched shapes**: A box collider for a spherical object causes unrealistic interactions. - **Overly complex colliders**: High-poly mesh colliders strain performance unnecessarily. - **Ignoring scale/layers**: Colliders won’t fit the model, or collisions trigger with unintended objects.
To avoid issues, test collisions early and use simple primitive colliders (box, sphere, capsule) instead of mesh colliders for most prefabs.