Where can it be used?
Short answer - at any point of software development cycle, starting from early development and all the way into final deployment and support.
Development. At some stage, logging into console or file becomes not effective, sometimes pretty useless.
Early integrations. Multi-host distributed systems, are hard to put together. Proper logging saves time. Even simpler single process applications could be intricate to debug sometimes. Checking logs or seeing logs in real-time is the only way through quite often.
Final testing. Good centralized logging system is invaluable at this stage. It simplifies life to many people, makes it easy to track, detect and follow problems, assign bugs, refer to exceptions, etc..
Production. Unless you smell bytes and see threads, centralized logging can save real money to your company by detecting problems early and responding to customer requests sooner.
