SDK 1.1.1 - Difference between debug and non debug builds?

A debug build for a .prg can be up to 5x the size of a non debug build, so what's there that's used?

Will things like Sys.println() (to <appname>.txt) not work in a non-debug build? Will CIQ_LOG.txt not be written in a non debug build?

Is there more error checking in a debug build?

Is the debug stuff there for future enhancements to debugging and not really used today?

If someone is helping to test something, is there an advantage to providing a debug version of the .prg vs a non debug version?