Often in a CGI web application a user's session outlives several program invocations. It's important not to log a user out of a web application before the stated session time limit. Users are fickle beasts with a ravenous appetite for support techs. Please don't taunt them with easy access to the support department through a bug report.

For temporary files that really don't outlive a single program, File::Temp can give you an open file handle for a file that will automatically get cleaned up without predictably placing the PID number in the file name. Temp file naming collisions are a security risk.