User experience in an application is one of the biggest factors, if not the biggest, to its overall grade. No application should ever be given a passing grade if it is not responsive and has a sluggish feel to it. A JavaScript application has the chance to be on either ends of the speed spectrum because of the wide range of implementation options. There can be more than a few potential bottlenecks in a JavaScript application, and even more in an AngularJS application, which should be noted and approached correctly.
The biggest issue with any AngularJS application that uses the 1.2.0 and above branch is the digest cycle.
The digest cycle is an AngularJS-specific issue and is the cause of most speed-related issues. This is because of the thread-blocking nature of the working of the digest cycle and the issues when working with a lot of data.