I think the sample configurations should avoid using location-based layouts like %C, %M, %location etc.
That is, unless the sample demonstrates the location-based capabilities, of course.
The performance impact of location-based layouts is quite large (something like 5x slower), and I'd hate to give people the first impression that log4j2 is slow because of our own example configs...
Here is the sample File configuration in http://logging.apache.org/log4j/2.x/manual/appenders.html#FileAppender with my proposed changes:
<?xml version="1.0" encoding="UTF-8"?>
<configuration status="warn" name="MyApp" packages="">
<File name="MyFile" fileName="logs/app.log">
<pattern>%d %p %c
[%t] %m%n</pattern> <!-- avoid location %C in examples -->
As per discussion on the dev mailing list, there should also be a section heading somewhere called Location Information that specifically identifies each of the location patterns and discusses the overhead of each.