Hi Jeff, when you Activate a BOM, it allows users who do not have the permission "See Computed BOM" ticked, to be able to see the BOM.
So it gives you a bit of flexibility in that you can choose which BOMs to activate and allow only certain users and groups to be able to see them.
Let me know if you have any questions.
Thanks Gentlemen, much appreciated. Apologies for not responding sooner. Both answers have clarified my understanding, the penny has dropped.