Interview Question | Software Engineer | Is Unit Testing mandatory or a futile practice?

The interviewer would like to know your attitude towards unit testing and what level importance you give to it in your current development process. 

Ideally your answer must convince the interviewer that you are from a test driven development environment and you don’t consider unit testing as a process for the sake. The answer must logically conclude that the unit testings are essential for the overall testing process. It avoids bugs advancing to the deliveries by eliminating logical flaws coding errors. It also prevents regressions where bugs return that had just been fixed.