You won't be able to take a Blood Pack out of a connected workshop and put it in your inventory to heal yourself, but you can make a Stimpack with it. This means that you can't drink Purified Water that's stored at a remote location, but you can use it to create Vegetable Starch. The only way to access them is by using them in the crafting process. Even then, those resources can't simply be collected from the Workshop's inventory. The only remote resources that are available to the player, in settlements that are linked via supply lines, are those which can be used for crafting. I'll try to explain better, by my understanding, here.
The current accepted answer seems a bit unclear to me, and may actually be inaccurate.
