It is true when using the Max-OT principles you are striving for a continual progression of overload. That means once you complete 6 “good” reps with any given movement it is time to increase your weights by the smallest increment available. The key phrase in that last sentence is “good reps.”
What do I mean by 6 good reps? That means you are in control of the weight for all 6 reps and require very little to no assistance from a spotter to complete the last rep. If you are sloppy or really struggle to get 6 reps it is not a good idea to move up in weight just yet.
If you get too ahead of yourself with weight selection you will begin to sacrifice too much form and control. This will lead to an increased potential for injury and a greater likelihood of plateauing with your weights.
When you are training with the Max-OT principles you want to use the best balance of loose form and maximal weight, being careful not to expense one for the other. Remember that loose form doesn’t mean sloppy or out of control it simply means allowing your body to move naturally through the exercise rather than being too strict or rigid. You can get a great visual example of exactly what I mean by loose form while under control in my training DVDs.