TL;DR: It isn’t obvious, how Anki interprets Return while reviewing (what’s the default selection?). It makes more sense to require the user to select the result (Again/Easy/Good/Hard)
Why I hate this shortcut: Most of my cards contain an input form to require me to type in the answer. To submit my answer, I press Return/Enter. However, sometimes because I type very quickly, I happen to press the Return key twice in a row, which then puts the card away completely. And it does not seem obvious what the Return key does trigger (Again/Easy/Good/Hard/?). Because Anki seems to have easy understandable and logical shortcuts for all functions required in review mode, I suggest to remove this one, as it is ambiguous to the user, what it does, and is easy to hit by accident, also, because it can be also be used to turn cards without input fields as well.