This is even how I was taught to cut things in apparel design school…but it isn’t the best way, especially for knits! And? It’s especially odd to teach this way because in the actual real world apparel industry, we don’t pin to cut out or fabrics. Pinning can stretch the fabric out of place and cause issues when you’re cutting.
The best way to cut out knits is with pattern weights and a rotary cutter. This keeps everything flat and helps alleviate any stretching issues. 
You can buy pattern weights at most fabric and craft stores, there are also plenty of tutorials around the web for making your own – my favorite is buying large washers from a hardware store and wrapping a few together with colorful wire, yarn, is strips of fabric to make them pretty.
You can also really use anything you’ve got on hand that has a little weight to it. I know people use paper weights, cans of food, their cell phones. But my personal favorite is pattern dinosaurs.
