[strken]

As someone who runs interviews occasionally, when you're sitting in an interview room, you're not making an immediate decision whether the candidate is better or worse - that comes after the interview. During the interview itself, your job is to learn as much as you can about the candidate. The biggest problem for both you and the candidate is that you might get to the end of the interview and still not be sure whether they're a good candidate, and therefore have to reject them.

You've got two probabilities to work out, "how likely is this person to succeed in the role we're hiring them to do?" and "how confident am I in the previous number?" Side projects usually don't change whether you think the candidate is a good fit (at least for me), but they usually do increase your confidence in your prediction, and turn some no-hires into hires.