There is more than just the array join method to work with after all and not just with respect to the other array prototype methods. When using join often other methods will be used before hand, so maybe some more examples are called for with this one.
An empty string can be given as the argument to the array join method. Doing so is what I would want to do if I do not want anything at all to be between each element with the resulting string that is returned my array join.
The string split method is another method that comes to mind when dealing with the array join method as it is an inversion of the method. Where the js array join method will create a string from an array the string split method will split a string into an array of elements.
For some arrays something might have to happen before joining all the elements together. For example say you have an array of objects and you want to join together all the values of a single property of each nested object together. In this kind of situation the array map method can be used as a way to create an array of primitive values before hand, and then that is what can be joined together.
So the js array join method is one of many array prototype methods that I find myself using all the time when and where using it is called for. If I have an array of elements and I want to join them all together into a string then the array join method is there to do just that right away and allow me to continue on with my code.