Negative-match keywords prevent your ad from appearing when a search includes a keyword that isn't relevant to your ad. Using negative embedded-match keywords can be even more useful, as they give you greater control over which queries trigger your ads.
For example, let's look at a client that sells Toy Story merchandise. Although the keyword 'toy story' is highly related, they may not want their 'toy story merchandise' keywords to expand to the query 'toy story' as it's too general for their product. With conventional negative keywords, they wouldn't be able to just add the negative '-toy story' as it would stop all of their 'toy story products' keywords from showing. However, if they use the embedded match option of -[toy story], their ads will appear for 'toy story dolls' and 'toy story products,' but not for the single query of 'toy story.'
You can run a Search Query Performance Report in the Report Center to find the queries that your broad match keywords have expanded to. From there, you can decide to add the expansions as keywords to gain more traffic or as negatives to prevent any irrelevant expansions.
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