Sure. I know the story in the States the best. Back in the thirties, there was concern.... Certain individuals were seen to have taken positions in wheat and things like that, which was suspected of driving the price out of whack. It's not just that the price went high; it's the volatility, that they can push it up and push it down.
When they pushed it down, the wheat farmers were angry and so on. That created demands for limits to entities that don't have a commercial reason for being in that market; i.e., they're not growing the wheat or using the wheat to make other products, so they should have limits in terms of how much they can participate in the market. It doesn't eliminate speculation, but it does keep it in reasonable bounds.