It is better to have options from which to choose than to have no choice.

You interview for a job, but it does seem like the right fit. You should still do your best so the company makes you an offer. If you choose not to accept it, they still have a great feeling about you. They might even refer you to someone else.

If you are interviewing a candidate and decide they are not a good fit, you should still sell the role so the candidate wishes they got an offer. They might talk the company up and lead the right candidate to seek you out.

How many more options could you have if everyone who meets you is left with a good feeling about you?