The following functions may affect performance depending on the nature of the script: SendMode, SetKeyDelay, SetMouseDelay, SetWinDelay, SetControlDelay, and SetDefaultMouseSpeed.
Each script is semi-compiled while it is being loaded and syntax-checked. In addition to detecting some errors early, this also greatly improves runtime performance.
Here are some of the technical details of the optimization process (semi-compiling):
In addition, during script execution, binary numbers are cached in variables to avoid conversions to/from strings.