Defining Default Values for Parameters
Parameters can take default values that step in for any missing arguments. We can benefit from default parameters in one of three ways:
As a user of a function, we don’t have to pass in a value for a parameter if the value we intend to send is the same as the sensible default chosen by the creator of the function—resulting in less work and reduced noise/clutter in code.
As the author of a function, we can evolve the function signature more freely, to add a new parameter, without breaking existing code.