I have gone through the following article regarding the logging frameworks available for Java: http://michaelandrews.typepad.com/the_technical_times/2011/04/java-logging-reconsidered.html
The author has mentioned using SLF4J with Logback. How is that different from using Logback directly. Wouldn't it be better if one uses Logback directly rather than going for SLF4J, since Logback is built on top of SLF4J.
SLF4J is adding zero overhead to Logback since it is simply the interface that is implemented by Logback without any additional layer.
You should use SLF4J simply because...
The only place where you'd access Logback directly would be while (re)configuring your logging manually in an application. The need for this arises occasionally but even in that case, working with Logback would be restricted to a single class or even method.
As a rule of thumb: libraries should always use a logging abstraction while applications define the logging they are using, optionally accessing it directly.