"This is actually a hybrid of checkboxes and the more recent selection model. So you can use checkboxes, but you can also still use Ctrl or Cmd to select multiple items. Another one I like a lot, is to use Shift to select many consecutive items at once (click on the checkbox of the first file, scroll down and hold down Shift when you click on a checkbox further down the list, this will select everything in between)."
Checkboxes may seem unnecessary, especially considering that people rarely select multiple files, but they're a familiar interface element that's easy to use. Not many people know that holding down Ctrl lets you select multiple files, even though it's a standard feature in most operating systems.
{ Thanks, Cougar. }