I, too, have the Viking. 99% of the time I use the default setting (which might be 2????) for piecing and binding. I don't change the stitch for binding. Might change it doing pp'ing so the paper rips off easier or when using flannel, but that's about it.

When I attach the binding to the quilt, I use the default 2.2 (Pfaff QE 4.0) but when I fold it over to finish (if I use the machine) I lengthen the stitch a little, maybe 3.0. That is just my preference, I haven't seen that advised anywhere.

I started using the 2 setting for working on curved piecing and have never changed it back, I like the smaller stitch. It seams to make a neater seam when pressing.
peace

EDIT: Iforgot to say that I do go up to 2.5 when binding or sewing thicker fabric. The longer stitch works better through three layers.

2.5 on my older Pfaff

I piece with the machine default of 2.2 but quilt with 3 and bind with 2.5.

This was my thought. I seldom change the stitch length. I have a viking Rose. When you turn the machine off & back on again, it will return to the default setting.

I have better luck when I go to 2.5 or 3 for the binding because there are so many layers. Small stitches tend to pucker mine because the transfer doesn't seem even.