The dongle is a physical device that can be attached to TV and it's used to receive the data sent from the compatible phone. That's not an application, but AllShare Cast is an application that's found on Samsung phones. If you don't have a dongle, then it's safe to say that it can be uninstalled. Additionally, the application comes with almost every Samsung phone that has Android as primary operating system. If it has no use for you, remove/uninstall the updates and then disable the application to prevent it from updating automatically.