Really useful in my playlists of UK chart hits year by year (http://ghostfood.uk/music/#ukcharthits) because when a track isn't available (even as unplayable) I use this as a placeholder to indicate there should be a track at that point in the playlist (they are arranged in order of when the track first entered the chart chronologically). That said, 11 seconds is probably a bit too long though as these playlists contain hundreds or even over a thousand tracks and that can also result in a few hundred instances of the silent track in one playlist (the ultimate goal being to eliminate all of these by having all 'hit' songs on the service).
I've had a problem using these silent tracks: instead of hearing a silence I hear a fairly loud blast of white-noise. This is not the case when I listen through a Sonos speaker, but it is when I listen on my phone (through headphones) or on my laptop through the laptop's speakers.
This makes the silent tracks unuseable for me, because I listen through headphones a good bit of the time.
I would like to use very brief silent tracks (1 to 4 seconds) to introduce space between songs when the first song ends very abruptly, and I want there to be a slight pause before going into the next song.
i couldn't find this playlist so it wasn't helpful. however i found an "album" by mike vargas called sometimes which has several silent tracks of varying length of time and an applause track for after you finish your workout!