In this way, if two people are working together, they on average have to answer 8 questions between them. So it is more work to cheat than to just answer the questions. I have LOTS of short quizes. And I have them be for low points. At specific points, when I want to guarentee who is taking the test, I use a proctor.
Proctored tests are worth lots more than the online quizes.
Librarians, other teachers, local administrators, notoray republics can all be exam proctors. And so the end result of my efforts is that it is not cost effective to cheat. And so I don't see a lot of it. When you must gaurentee no cheating, you must proctor. Just like in face to face situations.