Portfolios are the sum total of all of the artwork an in a Workspace. Artworks are added into Workspaces within the Organization. When you add new art, you are adding it to one Workspace, even if you have multiple Workspaces.
Once your art has been added to a Workspace, you can now create Collections. Collections are different groupings of artworks within that Workspace. For example, maybe you really like photography by emerging artists, you could create a Collection called 'Emerging Photography.' Only users within the Workspace can see these collections. Even if your art is shared to your wealth advisor, they will just see the inventory.