I used the trimmer extensively in a recent project. I wanted to create a "music video" of short clips (about 7 seconds each) of video I'd taken of my son over the past six months. I had about 2 1/2 hours of raw footage, consisting mostly of about 3 and 4 minute scenes in separate .AVI files (captured with SceneAlyzer Live).
I would preview each separate scene in the explorer, then load scenes I thought would be useful into the trimmer, create a region of the 7 seconds that I wanted to use, and then click the "add to timeline from cursor" button to add that region into the timeline.
I found this much easier than adding each 3 - 4 minute scene to the time line, and then splitting and deleting the parts I didn't want.
The trimmer can allow you to set markers and regions in the media that are seen in the context of the entire clip. You can zoom in to see just the selected area like a regular source-viewer, but zoomed out you can see more.
Those markers and regions can be saved with the media, so you can open a new project and have the "sub-clips" already marked. A lot of NLE's don't support this (sortuva bin import).
The trimmer permits selecting just audio or just video, to take to the TL; and conversely, you can highlight an event in the TL and open the media in the trimmer and see exactly what part of the media is used for that event (it will be highlighted).
It has an annoying (to me) function where when playing and you mark an outpoint, the cursor loops and plays from the inpoint, rather than continuing on... making it hard to mark a later outpoint. My pet-peeve on the trimmer.
So, workfows could include:
play and mark a region, paste to TL... mark a region, paste to TL...
mark and comment regions through the whole clip, drag in order of preference after
mark and comment regions through many clips, use region view in explorer to sort and select.