It’s easier to share original timelines or intermediate renders. Sharing timeline-in-a-timeline can be a disaster waiting to happen. If the editor needs to make a change to an underlying timeline because Legal dropped a last-minute bombshell, then the colorist’s grades can get shifted or lost since they weren’t tied to the actual source clips. Some tools have a way around this. Shotcut does not.
“The industry” is not the best way to approach Shotcut because it isn’t made the same way as those tools. New tool means new process. With Shotcut, tying grades to the source clips gives the greatest flexibility for future emergency edits.
Also in Shotcut, if a change is made to an underlying MLT that affects its duration, that change will not ripple up to the aggregating MLT. This means the higher-level MLT requires constant manual attention to make sure it is up to date with all the lower levels.
Yes. However, I’m not sure I see the advantage of this method. If the MLT segments are finalized and rendered independently, why not stitch the rendered segments together into the final movie? It is lossless to do so with ffmpeg command line, since script is involved either way.