I always forget about this one. And then I remember again, and like it a lot.
To preview files from the browser, there’s actually no need to turn on the Preview switch:
Just highlight the file you want to preview and hit the right arrow on your keyboard. This turns on Preview for the current file only. As soon as you move off of it, Preview turns off again.
The right arrow also comes in handy even with the Preview switch turned on. Pressing the right arrow causes playback to start over from the beginning of a file, which can really come in handy for previewing longer files or entire songs.