DDM is Dialogue Disabling Manipulation, and it's used to disable in game dialogues, entirely skipping Earnest's speech during The Candidate and other "free roam cutscenes" as well (not the FMV cutscenes, those still have to be skipped manually). During the speedrun you'll notice that runners will usually activate it at the beginning of a chapter and then deactivate it before entering a new chapter, that's because if you go into a chapter intro cutscene, while DDM is active, the game will softlock into an infinite loading screen, since it won't be able to process Jimmy's dialogues, and you'll have no option but to close the game and open again.

Here's a video for a detailed guide on how to do it and when to do it during any% speedruns