Windows Explorer Copying Files

When I use the right mouse button to drag a file from a folder in the right
pane to another folder in the navigation pane I see a + symbol in front of
"copy" now in Vista's Windows Explorer. Once I have settled the cursor over
the destination folder this will pop up. Is there a key that can be pressed
when this shows to confirm the file copy? Is this meant to make file copying
more accurate and less "chancey" depending on the users mouse ability