Rich snippets, often enabled by adding structured markup to your code, can potentially add stars, images, videos and so forth to the search results you see on Google or Bing. The richer user experience often leads to searchers paying more attention to the search results with the rich snippets versus the basic snippets.
Blue Nile Research claims that rich snippets in position 2 will have a 61 percent click capture rate, whereas no rich snippets on position 1 would have a 48 percent click share. This is compared to no rich snippets in position 2, which would result in only a 35 percent click share. So there is a 26-percent increase in the percentage of clicks the second result sees, if that second result has rich snippets.
Here is the chart:
You can download the full study over here.