Tracer  simplifies enabling the logs for specific category at specific level and only for specific request. It provides a very fine level of control via config provided as part of HTTP request around how the logging should be performed for given category.
For e.g. determining what nodes are written for a given POST request can be simply done by including an extra request parameter "tracer"
One can also specify actual categories as part of request param itself. For complete details refer to  (docs to be moved to Sling site)
Refer to  for related discussion