I'm going to take a beat here and shift gears and talk about why I changed from allowing player declared rolls to only allowing DM requested rolls.
The short form is that it's made me better at my craft as a DM.
Now, before anyone gets up in arms about me saying they're not a good DM for allowing player declared rolls, that's not it at all. It was a choice I made about what path I wanted to follow as a DM -- how I wanted my style to work -- and that switch has done a good bit to improving how I present my game.
To elaborate: I noticed in my games that I was gating information -- I was expecting players to declare rolls for things, so I gated information expecting those rolls. If/When the player asked for the roll, and succeeded, the information would be provided. This caused a number of problems that took me a long time to notice. Frustration on the players part on failed rolls. Frustration on my part on failed rolls. Time wasted "pixel-bitching". And, as a big one, unclear goals -- my players weren't clearly stating what their goal (or were stating intermediate goals) and were just trying to throw whatever they could think of to accomplish them, leaving me adjudicating approaches without being able to help achieve the goals.
When I finally put my finger on it, I resolved to change things. I also saw this exact same thing occurring in other games, where I wasn't running. But I also saw some games where it didn't happen. I resolved to improve my delivery. I stopped gating information -- instead providing more and more outright as I worked on changing. But, my players still kept asking for rolls -- they still had the mindset that there was hidden details that could be teased out with the right successful roll. So, after a little bit of this, I started changing how rolls happened at my table. Now, there's still a bit of adjustment for new players, and some of my older players still have some ingrained reflexes, but it's improved -- my players are stating goals and approaches.
And this has helped me achieve what I wanted from my games but was failing to realize: clearly stated, engaging scenarios where the players are focused on solving a problem and not applying mechanics. Still, my biggest issue is getting players to clearly state end-goals for approaches and not just an intermediate step along their grand plan that's still hidden in their heads. I think some of them feel (and it's only some, they others are fully embracing and find it liberating) that I'll foil whatever plan they have. To be fair, this comes up sometimes because I failed to provide a key piece of information that their plan hinges on because it wasn't something I had thought of before that point, and sometimes that piece of information can't be easily changed to support the eventual unveiling of a plan due to other, as yet unrevealed, pieces of the story. But, I'm pointing out that letting me know what the actual goal is means I work with you to see it happen, and adopting a fail-forward approach to these issues is helping a great deal. Getting there with the understanding that we will never be there, as this a process and not a destination.
So, yeah, that's why I don't allow player declared rolls anymore. They were causing me problems by having players think in terms of mechanical steps and not approaches and end goals. To be fair, player declared rolls are not incompatible with clearly stated approaches and goals, but I find that, at my table (and a number of tables I've seen), they tend to reward a playstyle that doesn't engage in clearly stated goals and approaches. YMMV, and that's awesome.