You had a candidate you really liked. The candidate really liked you, but decided to take a different position. That was 2-3 years ago. You have an opening now in your group, and this candidate pops into your head. What do you do?
You contact the old candidate, that's what! This is why you keep those resumes around in the horrible candidate tracking system. This is why you offer to link with people you like on LinkedIn. This is why you don't burn bridges with people, even if they don't accept your position. This is why you always say, “Oh, too bad. Let's stay in touch. Do you have a friend or colleague you can suggest who might fit with our culture?”
This candidate is called a “passive” candidate by recruiters. You can save yourself a ton of money and time. People often look up around 2-3 years and say, “Hmm, is this the right place for me?” Or, the company has trouble. Or the project gets canceled, and management is crazy enough to lay off the people on the project, not necessarily the people who are the most capable. Whatever the issue, you can take advantage of the potential candidate, not by a hot pursuit, but by checking in.
Send an email with a, “Hey, how are you. I was thinking of you when we had an opening that might be perfect for you.” It's nice. It makes a candidate feel all warm and fuzzy inside. And, if the candidate is thinking about looking, the candidate will think about you first.
Not only that will make you feel all warm and fuzzy inside, you might get a candidate who turns into an employee with no muss and no fuss. Passive sourcing at its best.