Some people like seeing the funny number go down. And it convinces people that FSRS is doing something other than voodoo magic.
But aside from that, is there really a reason to keep “Evaluate” or should it be removed?
Clone your presets and and click Optimise, if you get new parameters you’re better off, otherwise just discard the changes.
Also, I’m not going to vote as I don’t have any strong opinions, plus there are better things to remove if we want to simplify UI (historical retention e.g).
This is a good enough reason. In the scope of Anki – FSRS is still brand new technology. If you want more people to believe in and/or trust it, you need to give them a path to that.
[The second best reason is that for helpers, it’s the fastest way to tell if a user is reporting something that could be an actual issue with FSRS, or just complaining about how different it is.]