Web application monitoring is a crucial part of maintaining a high-performing and available web service. At its core, web application monitoring involves the consistent tracking and managing of an application’s performance to ensure optimal functioning. This procedure provides necessary data on potential issues that could negatively affect user experience, and lets developers proactively address these glitches before they escalate.

One key aspect of web application monitoring is the evaluation of server performance. Servers are the backbone of any web application, and their ability to process requests accurately and swiftly has a direct impact on user experience. Through constant monitoring, developers can identify and rectify server-side issues like slow processing, ensuring uninterrupted service delivery.

Web application monitoring also deals with transaction monitoring, an aspect that ensures all processes completed on the web application function as they should. These transactions could range from user-registration or login to checkout in e-commerce applications. Any hurdle a user faces during these transactions could lead to a sub-par experience or even loss of a potential client. The goal of transaction monitoring is to mimic user interactions and identify issues or bottlenecks for immediate rectification.

Another crucial facet of web application monitoring is the detection and handling of application errors. Bugs and errors are an inevitable part of the web development cycle, and while developers strive to make applications as foolproof as possible, errors may still occur. Monitoring applications can identify these errors quickly for speedy resolution, preventing long-term damage like loss of users or reputation.

Web application monitoring also encompasses monitoring end-user experiences. This allows developers to have an idea of how users perceive the application in real-world scenarios. By simulating the paths and actions of users, developers can obtain insightful data on performance glitches and latency issues which may tarnish the user experience.

Furthermore, application dependency mapping is another key part of web application monitoring. Today’s web applications leverage various interconnected services, APIs, and external databases. Understanding and mapping these dependencies is vital in diagnosing issues that can cause application breakdown and quickly getting to their root cause.

In conclusion, web application monitoring serves as a powerful, proactive tool to ensure web service performance. Given the online nature of today's economy, the slightest setback in a web application's performance can significantly impact a brand's reputation and its bottom line. By foreseeing potential issues and exploitable vulnerabilities, developers can improve and optimize performance, providing their users with the best possible experience.