PKF. What is the point?

On most peoples' systems, they are hidden - that's an OS thing though, nothing to do with Audition. They are just as necessary now as they've ever been, but because graphic card capabilities are much improved, it's now much faster to recreate them when opening a file - unless it's a huge one. In this case you could be delayed by a few seconds, and if you have a large multitrack session it could possibly be quite a wait whilst they are regenerated, and they have to be; they contain all of the visual information required to display the waveform of your file on screen. They are not about the audio at all - just the way it's displayed.

If you are only working with a relatively small number of shorter files it's fine not to store them. If you go to Edit>Preferences>Media and Disk Cache, there's an option at the bottom that will stop them being saved if you take the check out of it.