For hiding and protecting seam allowances on a non-lined garment, the “French seam” method proposes to encapsulate them within a second, hidden, seamline, sewn first with the fabric pieces wrong sides together, before the actual, visible, seam locks them away; an amendable procedure that easily justifies the effort.
Though the baste stitches (white thread) are not stricktly necessary, fixing these lines by hand greatly helps the process when using slippery fabrics.