Lambda functions are generally useful when using functions like map(). The map() function takes in a list and returns its modified version based on some criteria. This criterion is passed to it as a function.
A Lambda function is used here to calculate the area of each radius in circle_radii. The Lambda function, which calculates the circle area, is passed to map() as its first argument, along with the circle_radii list. map() iterates through circle_radii and passes every radius to the Lambda function which returns its area.