Adsense prevue tool & filtering

I thought the ads that show up when using the Google adsnese tool either are on my site or will be but when the window that shows these ads is being discussed most sites I have read about it, it everyone says they are sample sites. If that is true then why get the urls from the select url potion and past them in to you competitive ad filter. So the bottom line on this part of my post is are these ads that show when viewing the tool ads on my site, some ads from my site or future ads on my site.

I used this tool for the first time to bock ads I saw were competitors in case those ads are or will be on my site a day ago and I still have competing ads running.

If this tool show ads on my site or ads that will be on my site and all you have to do is select the ads you want to block because I know ads change, how do we know how often to check our sites using this tool. I know you can hold ads 24 hours but so you can block them but Google says I might not make as much money as letting them on my site right away so if the pries tool shows ad on my site or future ads I will try it for now, especially if there is any kind of regularity of when ads change.

Bottom line is what is meant by saying the ads that show up in the preview tool are sample ads. Are they actually ads on my site or are scheduled to be on my site even thought the term sample ads is used,

Is there any kind of schedule or regularity to when ads appear on my site if I continue to use the preference letting ads show immediately is it or where can I find it if there is such a schedule