Norton Internet Security 2010: Optimize Link

Good Afternoon:

 

I have Norton Internet Security 2010 Installed on my computer.  I noticed when opening the Performance window that there is a link to the term 'Optimize.'

 

What does 'Optimize' actually do?  How often should one run 'Optimize'?

 

Thanks,

 

John

 

Windows XP MCE 2005 SP3, NIS 2010, IE7