From the private sector, it is cheaper for a guy to retire, take his pension, and come back to work and not be in the pension when he comes back. A lot cheaper to do a match vs continue to accrue pension liabilities. The person no longer adds service to their pension, no longer grows their final average earnings. The sticking point is the guy usually must be gone from the company a decent amount of time before you rehire them. Otherwise, your plan could be in hot water compliance wise, like you're gaming the system to give him his retirement.