Yes I know but its not brought up every time it would be useful is it? You would use it every episode! Its ignored/forgotten about because it is an easy way out. Borg destroyed 40ships and killed 11000 people... lets slingshot around the sun and go back and tell them not to bother attacking! Apply same thinking to every episode. Now we have transwarp beaming in two movies back to back and I fully expect it to crop up in the third! Even though it has gone well beyond the realms of established Trek physics.