Generic Lots - What are they?

This was always my understanding: A lot type usually has requirements because the game is coded to have Sims behave a certain way there. E.g. a bar requires a bar, Stereo and TV, because Sims are coded to show up there and use those items, get drinks, dance, watch TV, different interactions. A generic lot has no requirements, therefore no coding. It also attracts no other Sims for this reason, they would just be standing around and/or all using the object on the lot that is the most fun and there would be no variety in their behaviour.