Here's how I use Subclips, on Sony VMS 8.0d (Build 139) Platinum
1.) I open a piece of video in the Trimmer.
2.) I mark a region by setting an In-point and an Out-point.
3.) I make it a region by hitting the "R" key, or the Insert/Region menu.
5.) I right-click on the Green Region indicator, and select "Create Subclip".
Subclips are useful for extracting the good-content from a longer piece of mostly junk-footage.
I find it useful to make the subclip a bit longer, on both the front and back, than the good-footage. I do the final, precise trimming on the timeline, but the subclip provides a good starting point.