Just like Comp said, the reason those larger planes are so long is so that you have more flat surface to register on. Being mindful that you would presumably have your stock firmly set in place AND you keep the plane flat on that workpiece! This is when you want to have a really solid bench to plane on. The bench would have clamps and dogs to keep that workpiece rock solid and then it's up to your body mechanics to keep that plane in check. I guess the best way to answer your question is practice practice practice!
Naturally to me having a Jointer in my shop is an essential piece of equipment. That Jointer along with my little lunch box Dewalt planer, my table saw and bandsaw allow me to have a smooth running shop. I personally don't use a Jointer hand plane but rather a power planer but it was a needed tool for me and allows me to make rough stock square and even save some cash in the process!