Protected assets prohibit users from diving into the network. Protection also prevents users from recreating assets by copying nodes and secures your asset from distribution. Protected assets do not allow editing of nodes within the OTL, so all relevant parameters must be promoted to the top level.
Open assets are not copy-protected and allow users to dive into the network and see each node. When you download an open asset, you are essentially downloading the "source" and are able to see exactly how the asset works.
The protected/open status of an asset is visible when you mouse over the download button. There is a dropdown menu which displays a lock icon just to the right of the asset price. an open lock indicates that you can dive into the asset and see how it's made.