Kits open up a whole other dimension of inventory tracking for your workshop. In principle, it allows you to associate 1 stock item with many other component items so that the set can be used as 1 unit. For example, say your workshop builds machines for your clients and each machine uses up a certain number of components which you buy in and track in stock separately. When you invoice the client, you want to invoice them the whole machine as a unit but still have the individual components tracked accurately. Kits allow you to do just that.
To create a kit:
If kit A was built from 2x component a, 3x component b then if you build 2 kit As, 4x component a and 6x component b will be deducted from stock while 2x kit A will be added to stock. Take care that you do not let the component quantities go negative as this may cause problems in stock tracking.