Many organizations have a set of materials (especially spare parts) that are considered critical.
You use these parts to maintain units that are especially important to your operations.
For example, if your company would be severely hurt by a breakdown in a production line,
the parts used to maintain that line may be considered critical parts.
Obviously, you want to make sure that you always have an appropriate supply of critical parts on hand. This lets you make repairs as soon as possible, rather than putting your operations on hold while you're waiting for parts to be delivered. You therefore need a way to indicate which items are critical, in order to distinguish them from materials that are less important.
In MainBoss, you could do this by creating an item category named CRITICAL, then assigning this category to all appropriate parts. If you do this, however, you can't specify the sort of information that the item category usually provides. For example, suppose that a particular type of belt is critical; all your other belts are put into a category called BELTS, but the critical belt must be put into the CRITICAL category. This means that reports on BELTS don't include the critical belt. Confusing!
A better approach might be to create a special critical storeroom inside each real storeroom. For example, suppose Room 101 is a storeroom which contains some critical parts. You might create a new storeroom called CRITICAL: ROOM 101 which is located inside the main Room 101 (which means that the 'Location' field in the critical storeroom record indicates that the critical storeroom is inside the main Room 101 storeroom).
Physically, the critical parts are simply stored in their usual place in Room 101. However, putting them in the special 'sub-storeroom' makes them easy to identify in tables and in reports.