Yes, a quick sanity check is useful when the calculation materially affects the recommendation.

The goal is not to prove every arithmetic step twice. Use a check when the number is error-prone, surprising, or central to the case.

For example, after calculating unit price from revenue divided by volume, multiplying the result back by volume can confirm the order of magnitude.

Keep the check short and explain what you are validating. case interview mental math guide.

I do this when the number looks weird. A five-second check has saved me more than once.