Plan in advance to fill vacant posts

In any organization, manpower attrition is a continuous phenomenon. People retire and new persons fill in those posts. However, there will be a gap when we do not get persons as skilled as those who retired or moved out. It may be difficult to find who will be resigning, as generally, we do not get information in advance. However, we know who is going to retire as per the organization's service norms. If we fill the posts after the retirement, then there will be skill gap and plant operations will be at risk. 

To avoid such issues and also to take care of attrition due to resignations/deaths, it is better to have a reserve strength (like bench in software companies) to make use of these persons any time as the need arises. 

Therefore, it is always preferable to have posts, say 5 % of total organizations strength, particularly in technical field as reserve/bench. The cost of maintaining this reserve strength with needed skills though, may appear costly / avoidable to the finance managers, will prove to be advantageous when we are in neck deep trouble because of lost productivity, or regulatory issues arising from incidents resulting due to poor skills of freshly recruited persons employed in place of experience hands, etc.

Afterall, one can't compromise with safety.