Comment #10 on issue 2653 by [email protected]: Midi output does not respect tied notes
http://code.google.com/p/lilypond/issues/detail?id=2653
In printed music, ties tend to be placed more between noteheads, and slurs across them. That way, ties usually fit reasonably into slurs. Also, if slurs are placed between chords, you get one, at most a double slur (above and below), whereas with tied chords, every note of the chord gets tied to the next.
If you take a look at <URL:http://www.wimmercello.com/bachlute.html>, you'll see a lot of slurs, but also at the start of the Allemande there is a tie. You'll see that the slurs are long sweeping lines and the tie, in contrast, is a small thing between noteheads with a lot of curvature, almost like an accent.
Now this is a rather sloppy handwritten autograph of Baroque music, and yet it makes the distinction quite discernible. In engraving, similar or partly even the same stencils are being used, but even then you'd place ties and slurs differently and pick shorter stencils for the ties.
