It is a colossal waste of time. Most of the time, you go in territories. When you get a territory, you work all the doors in it. Those where no one comes to the door are listed on a slip of paper. Next time you go into that territory after it's finished, you get just the numbers on those slips that end up with the territory (I have seen a few where only one or two numbers got scratched off the list on the first working). You go into the territory to work those numbers until you either scratch off every number from the list (which is rare) or you get no additional results. At which point, you destroy the not at homes and return the territory for the next person to do again. Nothing reduced! If you get a call, chances are good that it will fizzle.
As for the calls, I have seen witlesses with call books containing 40 or 50 active calls. Usually, they will get about 50% of those not at home. When they do get someone home, they usually discuss the rags and place a new set of rags. Sometimes, they will place the Washtowel Teach book, and attempt a study. Normally, that's the end of it because they keep having something come up.
And, when you do get a study, it is usually a time waster. I have seen plenty of studies in the Suffer Forever book where they reached chapter 16 or 17, and still have yet to attend a boasting session. And that was before the Internet. Usually, something comes up or they don't want to give something up. I have seen them sticking on giving up their church, smoking, living with an unmarried partner, and that they don't want to waste all their time doing the exact same thing. They can and do reach the end of the book without having attended so much as a single boasting session. They end up moving, and then they become someone else's problem. And that's when they don't snake-work the calls.