You never know if or when that person will become your client contact. After the placement follow up with phone calls every couple of months to see how they're doing. Your continued rapport building combined with the fact that they'll feel less emotionally tied to their former organization is a recipe for endless referrals. Sometimes they know their competitors strengths and weaknesses better than their competitors know themselves. That could save you a lot of time and time is money.
Good colleagues are rarley forgotten.
If you are restricted to dealing directly with HR try to get permission to speak with hiring mangers directly. You will learn a lot more about your search and add a few more contacts to your preferred list. Firstly, become a member in an association related to the profession type that you recruit. Get involved by offering free advice to members about your expertise in their field. Offer to be a guest speaker at meetings or contribute to the organization's newsletter on topics like career networking, how to write a better resume, how to plan a career strategy, and so on.