The Empty Action Node has no particular functionality other than organizing a complex module. You will encounter many cases where a module will become complex, because there are a range of options which a user can choose. This could be a different calculation of income tax depending on the user's place of residence. Or perhaps the user will be guided to a set of follow-up questions depending on their interaction with the module. Finally, all users may interact with part of the module containing more general questions. An Empty Action is a convenient way to bundle all the different paths in your module.
Multiple paths in a module can be bundled using an Empty Action.