When a mobile app visually responds it assures the user that it's working. And when it doesn't the app owner might lose a potential active user. Can you wait for 5 seconds for a cute picture to load? Maybe yes. But can you wait for 5 seconds to check a train availability you need to catch asap? Not really. Such wait time only brings criticism to your mobile app and a huge downfall on the user number.
Here's an infographic on "How Important Is the Visual Response by a Mobile App?" TechAhead recently interviewed few UX designers, and everyone has their own opinion.