Bleach free disk space with Norton Utility 16

Hi there

Recently I added NU 16 to my program, and I am starting to get used to it and like it yes! None the less I have a question regarding the use of NU's free space bleaching.

It says at the beginning, "disk bleacher will scramble your master file during your next start up" ; I did not dare to go ahead because I have No idea what this means indecision

could you please help me with the explanation? Is there any thing that could make a problem to my Pc?

It would be nice if someone give me an easy explain.

Thanks in advanced

Rab 60