Monitoring your web application is essential for professional maintenance and development. Especially if you have a high load on your website and you want to keep the current users on your site, you definitely should stay alert for problems and be able to react fast in case of problems. Monitoring is also crucial for A/B tests, since you have to evaluate somehow which version of your website performs better. Many big players also measure constantly how much revenue the website produces. For them it is important to monitor if a new feature increases or decreases the revenue and take decisions based on that information.