Fill-in work is work that is very simple, can be started, stopped, and re-started with little loss in effectiveness, doesn't involve other crafts and has minimal or no impact to the Production Department.
Examples of Fill-in work are:
• Routine inspections that do not require the equipment to be shut down
• Equipment repair/PM that is not Production related
• Repair of spare equipment
• Safety and other types of training
• Etc.
Having a small backlog of Fill-In work is a very valuable tool in managing the overall effectiveness of your employees and your P&S system. Fill-In work is not "busy work"; it should be work that needs to be done and adds value. Fill-In work will serve as a cushion for the remainder of your schedule. If your organization is very reactive, you may find it advantageous to have as much as 20% of your labor scheduled on Fill-In.
Tip excerpted from Planning and Scheduling Made Simple by Ricky Smith and Jerry Wilson