Hi! As an Amazon employee who interviewed and hired a lot of people here, I've created a guide that has all the questions and winning answers from an Amazonian recruiter perspective. Please check it out at interviewjoy.com/services/interview-process-details/amazon-senior-manager-interview-questions/ . Pls also check the positive feedback at the bottom of that page! Thanks.
First of all to prevent re work and manually execution errors. Which make the team have more time to othe duties such as continuous integration or product anylisis. Also you can run different tests suites according to the stage. Smoke, system, interop, regresion, etc