namespacesat your discretion (you control them, not your users). Namespces can be used to organize groups of functions designed for different use-cases within your product.
audit, it would make sense to create a namespace for each. If you wish to display a list of functions in your application UI, these namespaces would allow you to list only relevant functions.
defaultnamespace is always available if you don't wish to define multiple namespaces, and is especially useful when experimenting with or testing Compute.