You might want to check out the words of Wal-Mart's recently retired Executive Vice President and Chief Human Resources Officer on the value of long-term associates according the The New York Times:
"In the memorandum, M. Susan Chambers, Wal-Mart's executive vice president for benefits, also recommends reducing 401(k) contributions and wooing younger, and presumably healthier, workers by offering education benefits. The memo voices concern that workers with seven years' seniority earn more than workers with one year's seniority, but are no more productive.
To discourage unhealthy job applicants, Ms. Chambers suggests that Wal-Mart arrange for "all jobs to include some physical activity (e.g., all cashiers do some cart-gathering)."