APM (Application Performance Monitoring) tools offer end-to-end visibility into application interactions, providing actionable insights and golden signals such as error rates and latency. However, APMs can slow down applications due to auto-instrumentation, which adds code to the original application, creating overhead in terms of response time, CPU, memory, and network usage. Measuring this overhead is challenging, but it's essential to consider its impact on user experience and application performance. To mitigate these effects, developers should carefully evaluate APM tools, monitor their application's overhead under load testing, and consider data aggregation methods to reduce network traffic.