As Google App Engine for Python users, we have some reporting logs within the system that are already quite comprehensive and great for debugging.

When a team member decided that it was a great idea to implement rollbar, we were absolutely amazed by how much more comprehensive the error logging became. We can find very detailed information that GAE could not provide, such as request headers.

Also, it generates a report on each error and how often it happens. This makes it easy from a quality assurance and product management perspective on which errors that we should fix first. Additionally, it allows us to fix errors that customers have not reported.