The Match button allows you to select which Match types (Exact, Phrase, Modified Broad, and/or Broad) you wish to have the keywords in.
How to use it:
Select what additional Match Types you wish to add to your keywords.
For example I would like to add Phrase and Modified Broad to my keywords
After clicking Save I can see my results.
Here are the keywords in modified broad:
And if I continue to scroll down I see the keywords in the original Broad match type as well as the Phrase match type.