In a tight labor market, characterized by both low unemployment and increased mobility for workers, retention becomes the main method of building and maintaining a highly productive staff. If you can't keep your best employees, HR becomes little more than a treadmill engine.
And that's the best-case scenario. The worst-case scenario includes a steady decline in your team’s overall talent level, marked by near continuous recruitment, complete with all the annoyance and distraction that entails.
In short: You enter complete business purgatory.