Particles are like "Chapter Excerpts" that link back to the original media file. What particles will do is give you the ability to play (and tag) these excerpts as if they were individual tracks. As an example, if you have a concert DVD or a music video DVD collection, you can create separate particles for the musical tracks and play them individually, or in a playlist. I've done this with several of my music DVDs and it works perfectly. Since I still have the original DVD, I can tag and sort these as music tracks and cue them up accordingly.
Also, it is a "non-destructive" edit. Since DVD video is highly compressed, each time you reauthor it the quality degrades somewhat. Since particles don't reauthor anything, but simply link back to the original footage, there is no quality degradation, no matter how many particles you create.
As regards Chapters, there is an option in particles to create a particle for each chapter in the DVD, so that instead of a DVD menu you can play the DVD as tracks, and use the MC interface to navigate the DVD. Again, everything links back to the original.
IMO, this is really exciting stuff!