Most quilters do use the technique that you are describing to make HST. If you are making scrappy ones, it is easiest to cut the size of the finished squared plus 7/8" (most of us just round up), draw a diagonal line and stitch a 1/4" on each side of the line. Now, if you are using the same fabric such as with making a Carpenter's Wheel, you may chose to draw out the squares and diagonally lines, sew on both sides of the diagonal lines and then start cutting on the lines of the square. There are rolls of paper printed grid called Triangles on a Roll that eliminates all the drawing making it much easier. Hope this answers your question..