Haven't used it myself but from the help:
You can invoke a script at startup or run a script using either the SCRIPT or the SCRIPTCALL command. The difference is that the SCRIPTCALL command can execute nested scripts in addition to commands. With the SCRIPT command, if a script is currently active when the SCRIPT command is invoked, the script is stopped.
Basically allows one to nest or chain scripts (like the call command in batch files). I typically only use scripts generated by, and invoked from LISP. While I've never been tripped up by the lilimitation of SCRIPT, its sibling command may prove useful some day. Thanks for the heads up Marc.