The classic version of Yahoo Mail has a new feature: a better search experience. Yahoo shows in the sidebar a list of senders, attachments types, dates and folders you can use to refine the search results. For example, if you search for "meeting", you'll see a list of contacts that sent you emails that contain this word, so it's easier to restrict the results only to some of your contacts.
Yahoo also offers an easier way to view your attachments. There are two new views for the search results: "photo view" (that shows thumbnails for the attached photos) and "attachment view" (that shows information about all your attachments). You can select some of the attachments and download all of them in a big zip file.
The informations are useful because they give you the big picture for the search results. Gmail has advanced search features, but it's hard to know a priori all the details about the results.
It's interesting to note that the new features aren't available in the new Yahoo Mail, that has a very weak search. Also not all the classic accounts have the new features. If you use Yahoo Mail Beta, you can switch to the original version by clicking on "Switch back" next to the logo from the top of the screen. To go back to Yahoo Mail Beta, visit new.mail.yahoo.com.
The new Yahoo Mail, slowly released