I've used it to:
hand baste to eliminate pins (when I know a project will take awhile, I hate it when a pin leaves a mark)
anchor down applique pieces for travel work (to eliminate pins and hold in place)
SID to hold larger quilt firmly together so I can do my pretty top stitching with no worries
Trapunto work, so I can stitch, trim batting, then topstitch with nice threads but hold that trapunto batt secure
Also used for holding down applique pieces while machine embroidering ~ some designs I can see that extra layer of thread as a bulky bump under my satin stitches... this water soluble washes away after a good soak, and eliminates that hateful bump :)