The tool giving a quick answer should leave room for the user to understand its limits.

An answer that arrives instantly carries an implied confidence it may not have earned. Speed and certainty feel like the same thing from the outside, so a tool that hands over a clean result without showing where it is guessing has told you less than it appears to. Knowing the edges of an answer is part of the answer.

Ask what a quick result does not cover before you rely on it: which cases it was built for, what it does when the input is unusual. If you make such tools, say so plainly in the output rather than in a manual nobody opens.