Well, since no one else has answered, I'll just jump in here with a WA guess. Bear in mind my machine was new in 1962. My guess is, if the second one is indeed for quilting, that it will handle multiple layers of fabric and batting and the first is for the more commonly used one or two layers. Like I said though, mine does ziz zag but only one selection. It does, however, have adjustments for heavier and multiple layer fabrics.

Hopefully someone else who is more knowledgeable about newer machines will enlighten both of us.