Quote Originally Posted by NichG View Post
Often, when this kind of ruling is called for, it has to do with something that isn't easily decided just by looking at what's written. The DM is being asked to write a new law of physics right then and there. Its hard to do that on the spot in a way which is going to be completely future proof against every situation that could come up, especially if its being done in a vacuum of knowing what sorts of situations the player envisions it coming up in. On the other hand, if the DM understands why they're being asked to write a new law of physics, it gives them a better idea of what particular consequences they need to pay very close attention to and be careful about, which drastically reduces the chance that later on they'll need to ret-con their ruling because of something broken or stupid.

To put it another way, in the absence of that information, the safest response that the DM can make for the stability of the game is 'no, you can't do that'. However, that's a very limited and constraining way to play. Giving the DM more information better allows them to sometimes say 'sure, and here's how it will work' without worrying that it's going to break things or that they're being tricked into something.
As long as we're giving credence to anecdotal evidence, I've never had to reverse a ruling, and I also never pump my players for information on what they want to do beforehand. Some rules combine together to have powerful results, and others don't; I always strive to make rulings that approximate RAI as best as possible, and that means not caring about the circumstances in which the ruling is requested. A ruling resulting in consequences is no different than a cut-and-dry rule resulting in consequences, but I don't go around changing those just because the players want to do something I don't like.