Advertisers lose a lot of money by not creating a proper structure for their campaigns. This includes the non-usage of negative keywords to avoid inter ad group competition. Let me give you an example.
Lets say you have two ad groups - one of them has buy mobile online and in another buy samsung mobile online. Both of these are under Broad matchType. When a user searches for buy samsung mobile online, both the ad groups will try to trigger ads and will unnecessarily increase your costs. To avoid this, we put a negative keyword "samsung" in the "buy mobile online" ad group.
Another scenario arises when you create single keyword ad groups. For example,
lets say you have three different ad groups for the keyword iphone repair. So we have +iphone +repair (Broad Match Modifier), "iphone repair" (Phrase) and [iphone repair] (Exact). Now +iphone +repair ad group is intended to trigger only when a user searches for a query like repair my iphone and not when iphone repair sydney, best iphone repair or iphone repair are searched. We have separate ad groups and keywords for phrase and exact keywords and it is best that the ads are triggered from them and not from the broad keyword ad group.
So when a user searches for iphone repair all 3 adgroups will compete against each other in the auction and increase the costs. AdNabu prevents this by putting phrase keywords as a negative in broad and exact keyword as a negative keyword in phrase. This results in the following structure: