This combined mode can be very useful if you keep tons of windows open, and/or if many of your apps use smaller windows that really aren't distinguishable in Exposé mode. (Notice, too, that Exposé now displays the title for every window; in 10.5, you only saw titles when you moved your mouse over one of the windows.)

Thanks to readers Benji Coleman-Levy and chumsdock for the observations on the new abilities of Exposé in Snow Leopard.