title: How long do the magento session files need to be kept?
body: <p>I have a customer who's magento session files are quickly growing out of control.  We are purging them once a week, but it seems that it may need to be more frequent. </p>
  
  <p>1) What do these files do?  How are they connected to the users online experience (e.g. if I delete them and the user is still on the site, how will they be affected) </p>
  
  <p>2) How soon can I delete them?  How long do the files really need to remain on the server? </p>
  
  <p>Chris</p>