Sometimes you need convert objects or .json to string, and well in.that moment .toString() is useful...

Let put it in specific cases:

• When I work with adding 2 number or adding 2 string

  var num1 = 25

  var num2 = 30

if I wanted to join 2 number to string 2530 then I would use num1.toString() + num2.toString()

• When I need to parse a JSON to a string:

when I need to save a request body (JSON body of course) for audit purpose, I can use toString() on that object and save that string.

And many more... (I will update if I think of something)