The following might be said of AI:
- As you noted, AI models can be a bit easier on frame rates if they are designed for that purpose. This can be accomplished by using lower resolution textures and such. In addition, AI versions don't need virtual cockpits and so use up fewer resources.
- Since AI models would only be flown against, their characteristics can be tweaked for better gameplay. One example are the flexible gunners on non-player aircraft, which some folks claim tend to be deadly accurate. Their gunning skills can be upgraded or downgraded as needed by engineering AI versions.
- Models built without a virtual cockpit aren't really flyable, so sometimes we just call them AI versions rather than incomplete.