How PWA can be useful rather than developing a Simple web Application

I know I am very bad at asking a question so please tell me rather than downvote me...thanx

Q1: How Is Progressive Web Application Useful?

Q2: What Type of Application Should be Built using PWA is there any Specific Application which contains a lot of CPU utilization or Simple Static Pages with just small interaction with Server?

Q3: What should be the Application Architecture? In General?