When it comes to search, a keyword should only ever show up once in an account. Having keywords in different places eligible to show ads for the same search query can lead to two key things. First off, the advertiser is bidding against themselves in the bid auction, increasing the amount they are paying per click. Secondly, a keyword or ad may perform better with the copy in one ad group than with another. Duplicate keywords lead the advertiser to lose their ability to control messages as clearly.
With the exception of the cases outlined below, do not use duplicate keywords.
– If a campaign is duplicated with different targeting (i.e. geographic or device oriented campaigns), it is ok to use the same keyword and match type in both campaigns.
– When using more than one match type, it is ok to use the same keyword with different match types as long as the keywords are in separate ad groups and query control is being utilized. (As in, all queries for the exact match are leading to the exact match ad groups while all broad match queries are leading to the broad match ad groups)