Sentence:  Putting on local musicians at this place in the program serves a triple purpose : it saves the top flight jazz men from being wasted in this unenviable spot , when the audience is cold , restless , and in flux ; it <WSD>prevents</WSD> late-comers from missing some of the people they have come a long way to hear , and it gives the resident musicians a chance to perform before the famous Newport audience . 
Meaning of the word marked with <WSD> tags:  stop (someone or something) from doing something or being in a certain state