I'm a big fan of starch. Even when I make half square triangles using the square, diagonal line, stitch 1/4" on each side of line method, I still starch my fabric until it is stiff. It helps stabilize the bias which can stretch even using the square method-- and I think you get nicer looking stitches with stiff fabric. Also, it makes it a lot easier to get good crisp pressed seam allowances if you are pressing to the side and that makes it easier to get everything lined up when putting together your blocks.
Rob