This is an HTTP status code and it serves the purpose of letting you know if your HTTP request to the web application was successful, redirected, failed, etc. in general, any code greater than 399 is a failure, and any code equal to or less than 399 is acceptable. Developers use these codes when automating processes involving APis and websites, browsers use these codes to tell users what errors are being found on websites, etc.
When I write code that "talks" to websites or APIs I always check the status to determine if an error has occurred.
