Sorry for the late reply - if you know that a product is a prepackaged one, you can treat it accordingly. Compositions are needed if you wish to include multiple products in the order based on a sale from a single product listing. So if you have an item which you know that it consists of other products - you can have such item, but you would always need to keep that in mind on your end. Having the composition set up will allow you to track which items are held in a composition and which levels they are taking from the child items. If you do not need to have that calculation - you can treat your stock items as needed manually. Of course when you sell such item - it will not pull in any child items to the order, just that one which was sold.
Is it possible for Linnworks to manage stock of our boxes without using compositions on the product?
For example product SKU item100 will always use box sku box100.