When working with an object, you don't always care about all of its properties. If it's packed in a certain way (tuple, Optional wrapper, etc.) that is easy to

When working with an object, you don't always care about all of its properties. If it's packed in a certain way (tuple, Optional wrapper, etc.) that is easy to unpack with destructuring, then you might use an underscore to say "this is how it's structured, but I don't care about the particular value it has so please don't bind it to a variable." If you bound it to a variable and didn't use it, it'd be the same as declaring an unused variable.