Last time I looked about 98% of the time I sew straight stitch. There are lots of times it is nice to have an extra machine set up for a task. An extra machine can be set up to just do one color thread, just do button holes with a button holer or just use a bigger needle and heavy thread - if you are going to do that you can set the tension for the heavy thread. You could use that machine and set another machine up just to do zig zag or some other stitch - it is easy to just go back and forth from one machine to the other. There are lots of ways to finish seams other than zig zag.
http://sewclassic.blogspot.com/2013/...er-french.html