AddHyd is used to add any number of hydrographs. There is no parameter associated with AddHyd.
A junction is primarily used to read the flow from upstream commands or connections, and no parameters are associated with it.
A junction is also a tool for accurately connecting downstream elements, especially when dealing with multiple outflows. The Junction is the go-to feature when dealing with multiple outflows and provides the flexibility to handle complex hydrological systems. They are added automatically when incorporating LID commands, which may have different outflows.
The following image presents a scenario for the usage of junctions: