Hi
if you clear the entries in the host file, the ads in the web page will actually connect to the ad companies website and the add will be shown on your webpage. Possible them might also have some popup and stuff like that. It will also place a cookie on your computer.
Having these in the list will avoid these stuff.
Read the last paragraph of the "Blocking web ads". The link you posted
The IP 127.0.0.1 points to your local computer, so you are effectively telling it that all these ad servers are on your own PC. Whenever your browser tries to retrieve an ad from one of these companies, it will look on your own machine and will fail. You're left with a blank area where the ad would normally be. It will also keep these servers from placing cookies on your PC, as you won't even be able to connect to their actual server. Another nice feature is you can update the list at anytime, and even undo changes at anytime (I'd just rename the file instead of deleting, in case you need to put it back).
