Quite often in a game I conquer an AI developped planet that has specific tiles, like bonus to population, bonus to economy, etc, being misused.
It may be that the AI was desperate and had to use these tiles for something else, or it may be that the AI is ignoring the tile's bonus. For example, a market center built on an influence tile. A research center built on a economy tile. Little stuff like that annoys me. I like efficiency, the AI does not seem efficient 
I'm playing on normal, so maybe it's only something that kicks at an higher difficulty level?