I agree with you the through-cut indicator is useful, and so is the ability to re-join the clips. But I have also discovered that there is a downside to this, i.e., the indicator doesn't tell me if one of the two clips have been altered (under Motion tab, or with filters). So I have to be careful with that. If I make a razor cut and intentionally change one of the two clips, I have to remember not to join that through-edit, otherwise I lose the change (if it's in the later clip) or extend the change to where it's not needed (if it's in the earlier clip). Also, I have made the mistake of applying filter to one of the two clips, and forgetting to apply it to the other one as well. Since the filter effect was fairly subtle, I didn't notice until almost too late that the effect "stops" abruptly and prematurely.
So yeah, I think it's a great feature to have, but has its pitfalls as well.