G Bryant McClellan (8/1/2012)
While every testing method negatively affects the performance of the thing being tested by making the tester part of the experiment, some are obviously worse than others. I'd be interested to hear from some of the SQL Internals authors if they have some insight into how SET STATISTICS TIME ON works and how its use may or may not affect other situations where it is used. Paul? Kalen? Are you thinking about this yet?
Having STATISTICS TIME ON causes SQL Server to measure things every time a T-SQL frame is entered and exited. The way T-SQL scalar functions are implemented now (with BEGIN...END syntax) an (expensive!) new T-SQL frame is created on every call.
http://blogs.msdn.com/b/sqlclrperf/archive/2007/03/08/scalar-functions.aspx
Paul White
SQLPerformance.com
SQLkiwi blog
@SQL_Kiwi