Another PS Instructor here, so feel free to take this with a grain of salt, but my approach is to look at any and all diagramming tools as just that - tools. It's my job to provide my students with a full and robust set of tools that they can bring to bear on the job of writing the test. It's up to them to decide which tools are right for them to apply to a given job. We teach the use of not-laws because many students find them useful. It's easy to decide to not use them once you have a good handle on how to do the games, but hard to come up with them if you've never been shown how they work! :-) For myself, if there are just a few, I use them. They tend to be a handy, simple reminder of a rule or an inference, and when there are very few they are often tested directly (especially if it's an inference rather than a rule). When there are many, I tend to avoid them completely and focus instead on the few things that can happen instead of the many that cannot.

At the end of the day, what matters is that you have the right tools to do the job well and the way that works best for you. Don't like the not-laws? Don't use them! We are definitely not trying to tell anyone that this is the only way to get the job done, or even that it is always the best way for everyone. Just that it's one way that might prove useful to some of you.