What’s the main purpose of logging? code example

Example: what do you use for logging

I use Log4J for logging. 
I always log important steps in the test
execution. That helps me to debug
when there is a failure.
Log4J is not a replacement for HTML reports.
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j- core</artifactId>
<version>2.11.0</version>
</dependency>