Match Types
Match types control how closely a search must resemble your keyword for your ad to be eligible - broad, phrase, or exact.
Why it matters
They determine the trade between reach and control, and the right setting depends entirely on how much conversion data the account has to steer with.
What people get wrong
Believing exact match is exact. It has matched close variants, plurals and synonyms for years. All three types now require the search terms report to police them.
Broad match behaves differently depending on what is steering it
Broad match with manual bidding and broad match with a smart bidding strategy are not the same product, and most advice about broad match fails to say which one it is describing.
With conversion-based bidding and enough conversion history, broad match uses those signals to decide which of the many queries it is eligible for are worth entering. Without that history, it is matching on language alone across a far wider set of queries than the keyword suggests.
Which is why the same advice produces opposite results in two accounts. A mature account with months of clean conversion data can run broad match productively. A new account, or one whose conversion tracking is not trustworthy, is buying breadth with nothing steering it.
Running the same keyword in more than one match type
Adding a term as broad, phrase and exact in the hope of covering everything usually creates internal competition rather than coverage, and it splits the conversion data for that term across three places - which weakens the signal each one has to learn from.
If you do run overlapping match types, the search terms report is the only thing that tells you which one actually served, and negatives are how you decide it rather than leaving it to the auction.