Performance is an important issue to keep in mind when designing web apps. Web apps that are unresponsive or that perform badly will eventually lose all their visitors. They will simply hop onto another site. Azure provides multiple options so that you can make your web app highly available and scalable, which will result in better performance to keep your visitors on board.
Besides the features that Azure offers to design for high availability, scaling, and performance, you can keep certain architecture patterns in mind when architecting your web app. You can refer to the following article from the Azure architecture center for these patterns: https://docs.microsoft.com/en-us/azure/architecture/patterns/category/performance-scalability.