Among other things, I have been trying to grasp the concept of Map Entities. Ok, why? If you could pretty much do the same things with a model, why should you use Map Entities? In Grimber's FPS tutorials, he has us create a pane of glass as a Map Entity. (I have not finished it, by the way.) Why not a model?

When should you use a model, compared to a sprite or map entity?
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Please help me defeat my seemingly indomitable ignorance...