I've seen both enthusiasm and scorn with regard to this terrain. I used to regard them a strict blessing at first, but reconsidered when I actually thought about them: Every flood plain worked is a good tile (the additional food compared to grasslands cancels out or surpasses the health penalty), every flood plain not worked is bad (pointless health penalty). Simple so far, now the implications: 1) Commerce cities: Wonderful. We can cottage early on without needing farms to grow into the size to work more cottages. Since we want to work all decent tiles, it's strictly superior to grassland outside of special circumstances. 2) Anything else: Double-edged sword. Later on, watermills (and possibly workshops) means we can grow these and still support a lot of hammers, and when we want to run specialists a few are still better than featureless grassland... but there can be too many. - If we have several food resources and immediate goals other than extreme growth, we will end up with unworked flood plains -> bad if health is a factor at all. - Early on, a moderate number of flood plains will allow faster growth than a high one, especially if we have jungles in the fat cross. Conclusion: Most cities benefit from a few. Having a lot is a questionable late-game benefit at best (unless health is no issue, say when playing an Expansive leader on a low-ish difficulty). Hence, splitting them up between several cities seems to be optimal if we have the choice.