Traditionally home sewing patterns are riddled with outward facing triangles. These notches serve as a marker on the corresponding adjoining piece to ensure the garment goes together properly when the notches match up. These little bits are especially difficult to maneuver around with a pair of scissors. Sure practice makes perfect, but I personally hate cutting and anything that can expedite the process is always welcome.
Traditionally mass production patterns have the same indicators, but sometimes for additional reasons. However, they appear slightly different. Rather than being outward triangles, they are small incisions perpendicular to the fabric edge cut into the seam allowance a little less than halfway. This makes cutting a heck of a lot easier because the cutting tools used for mass production can have difficulty maneuvering around the triangles and the additional effort to cut around these small bits is almost not worth it as it is slightly more time consuming. It is far more efficient to make the incision quickly into the seam allowance.
The only time you will find an outward triangle notch on SBCC patterns is if there is gathering and a notch is necessary to match to a corresponding point. When the fabric is gathered it is hard to find the small incision, so the triangle notch is easily visible. These notches are not as easily visible at first glance, but when you are working with a piece, they are easy to spot. So with these kind of notches I find the best method for speedy cutting is to cut out all of the exterior contours of all the pieces and then go back and snip all of the notches. Oh, and don’t forget- single notch generally refers to the front of the garment and a double notch indicates the back.