the additional parameter “rot=0” gives you the option to send this parameter to your function if you’d like to change it (use something else than 0). But if you don’t like to change it you can just ignore this parameter, since it is set to 0 already. In case you never want to use the rotation parameter rot, you don’t need it, but I showed it for an example of how you can add optional parameters (=parameters that you may use or not).
Usually, you need to send values for parameters that you define for the input of a function (as i and k in our example). That’s the most often used variant. But you can use optional parameters as inputs as well (after the obligatory parameters). When you call the function, you can decide if you change the optional parameters or not. That’s not possible with the “normal” parameters as i and k.