I’ll try to explain this to the folks that probably still don’t know what we’re talking about.
Let’s say I’m making a tough online edit and I need to manually edit and sync some shots in. The best sync point I find in the timeline clip is in the middle of it and then I’ll search the same frame in the source clip. Then when I make the sync edit the edit goes from the playhead (that’s parked in the center of the clip) to both directions stopping at the clip’s in and out point “filling” the clip with the source footage.