Jonathan Kehayias (@SQLPoolBoy) of SQLskills.com evaluates the performance impact of query_post_execution_showplan and explains why you need to be very careful about using it in a production environment.
As you have most certainly heard elsewhere, SQL Server 2012 finally offers a version of Extended Events that is a viable alternative to SQL Trace, in terms of both better performance and event parity. There are other enhancements such as a usable UI in Management Studio – previously your only hope for this was Jonathan Kehayias' Extended Events Manager.
SQL Server offers two methods of collecting diagnostic and troubleshooting data about the workload executed against the server: SQL Trace and Extended Events. Starting in SQL Server 2012, the Extended Events implementation provides comparable data collection capabilities to SQL Trace and can be used for comparisons of the overhead incurred by these two features. In this article we'll take a look at comparing the "observer overhead" that occurs when using SQL Trace and Extended Events in various configurations in order to determine the performance impact that data collection may have on our workload through the use of a replay workload capture and Distributed Replay.