Even though that track is in multiple playlists, there's usually only one copy of the actual data on the empeg. Deleting it will only save you the space of that one copy.

I say usually, because if you've loaded a bunch of content, and then organised it into playlists, this is what will have happened. See this page for a more technical slant. If you've loaded the same track multiple times, then there may be multiple copies on the empeg.