Advertisements aren't everyone's cup of tea, and whilst sites like Webica.NET now carry advertisements they can be easily switched off programatically.
Once you introduce switching options a number of possibilities open up, Google allows up to four Ad elements / formats per page.
If there are no lines of text in this left column the ads below move up here and if there is text in the right column the ads move to the outside right. A page with just a title and no body means both columns have ads
The result is that the ads position can move around automatically as the amount of page content is updated.
Technically ads are implemented by including particular JavaScript blocks for each of the formats you choose to support on you page(s), by placing these scipt blocks in Div tags which have an ID value and runat="server" attributes then you can introduce a number of switching options via .NET code applying new runtime styles
Whilst this granular tunning is desirable if you have programmatic control over these Ad-Div's then they can also be switched off on a page by page basis, or at certain times of the day or if you decide a particular pages content would attract to many to monitor or simply not warrent carrying any Ads!
The "quality" of some of the ads (e.g. £1000/wk home working) is questionable, and so I felt a follow on is needed, now
here.