String to Array is handy for testing when you need some sample data. Why bother adding ports to a Build Array node and typing in values, when you can just paste in a string. Depending on where you get the raw array data, sometimes all you need to do is a little search/replace magic in your favorite text editor, and then you’ve got a string you can paste into String to Array.
Note that the type of the array elements is defined by where you plug in String to Array. So if you want to put the array into an attribute, you’ve got to define the type of the attribute first.