A recent quilt I finished featured a lot of diagonal lines. I did not want the verticals and horizontals in the final pattern, but knew that I needed to stabilize the quilt prior to the diagonal lines in hopes of keeping it somewhat square. Water soluble thread was definitely helpful for that - allowing me to stitch near the ditch first, and then I could focus on the other long seams without issue. Same for the smaller in-block designs.
Cheers, K