The use of "cut" is a well known performance enhancement for Prolog-style rules. In KnowledgeWorks it does more than reduce the time spent in search. When a "cut" is invoked, all the stack space between the initial call to the containing rule and the current stack location is reclaimed immediately, and can have a significant impact on the total space requirements of a program.
KnowledgeWorks and Prolog User Guide (Unix version) - 6 Dec 2011