TDD is an essential part of any software development cycle. Here's a story from my past which relates its importance:
I created a filter module for products just like amazon or flipkart have. I tested it well on my machine and it was working great. Then came the day of live demo to our client, where this filter suddenly stopped working! It was doing nothing in our staging env and it was kind of embarrassing.
The next day, I decided to create unit tests for each every function that I wrote. As developer we should feel confident in our code's ability to run well, therefore, we must learn to love the feeling of having a watertight app that comes with automated testing.
Apart from my stories let us start a real example. You can follow AngularUnitTestDemo on github or clone a local copy to begin with.