In software development, it is always good practice to include messages that indicate what the program is doing with clarity without compromising the efficiency of the software. The ROS framework provides a set of APIs to enable these features, which is built on top of log4cxx, a log4j logger library.
In short, we have several levels of messages, and all of them have a negligible footprint on performance and can be masked by the current verbosity level during compile time or even in runtime. Moreover, they are fully integrated with other ROS tools for visualization.