Hopefully, "real" users will reply, but here is my take. Recently I found a very nice introduction on linear editing for multi-cam.
I finally understood how it should work in Cinelerra GG. But it is not intuitive, I would like to propose two things that could make multi-cam editing much more user friendly.
<https://www.youtube.com/watch?v=rOMKP4Jgzw8>
1. As you can see from the video, multi-cam works by clicking on a Mixer. Completely counter intuitive towards anyone that works with a switcher (atem and likes) it adds video from the undecided point up to the current position when clicked on the mixer. This would be a feature request that I wonder why nobody asked for this: implement this in the opposite way. You click on a mixer A, then the timeline gets filled with that mixer (visible, or underwater). If you click on mixer B, the timeline is computed with the part 0 to timeline current position with Mixer A, and having Mixer B as start position.
It was probably programmed the way it is, because its usage was where you had multiple video recordings from different angles at the same time and the user wanted to pick the best one at that particular place. Like when recording a band playing with 3 cameras placed at different spots in the venue. Possibly your suggestion could be an alternative methodology but as for "If you click on mixer B, the timeline is computed with the part 0 to timeline current position with Mixer A", it might be very difficult to keep track of each tracks "part 0" as it changes to "part next start".
2. Now you have set up your rough cut. What you would actually want is the ability to fine tune. I would like to have a drag handle functionality that would be able to modify the cut position. It should be able to move to left or right. The limits of this operation are bound by the source videos. One can move to the left beyond the left video, but only up to the point that the right video has data. The same goes for the move towards right. At this moment you can never get this right with trimming or extending, especially not when there is an audio track to match it below. Hence I think this function would benefit every editor. (feature-mouse.png)
Maybe I do not understand, but there is a drag handle (in Cut and Paste editing mode) for fine tuning and it can be cut/moved from left or right. I tried to demonstrate this in: https://streamable.com/zfeuka The one thing missing per your suggestion though is for it to not go past where there is data. You should be able to use the drag handle to get exactly where you want to be by watching the Compositor window and then when you stop dragging, all of the small mixer windows update to that exact point.