The process of adding in negative keywords to a paid search account is an important part of the optimization process, as it allows for eliminating search queries which are unlikely to convert into a sale.
There are few automated tools to predict the negative keywords and make the process simpler.
[1] An additional use for negative keywords is to funnel traffic to the highest-converting and optimized campaign or ad group for a particular search query.
For example, if an advertiser is marketing laptop and desktop computers, and has ad copy that is specific to each, he may notice that some searchers who are searching for laptops are being shown desktop ads and vice versa.
Negative keywords can be used to make sure that each searcher is shown the most relevant ad copy that is most likely to convert into a sale.