A dialogue overlap is a technique that can help you accomplish a number of things in the edit.
- It can help to smooth over a jarring edit, or to avoid a bit of worrisome camera work
- It can help compress time or remove "air" in a performance
- It can help create a sense of conflict between characters
- It can be used to create an emphasis on the dialogue that is on character who's speaking
The reason why I hate arbitrary overlaps is because if your film is full of them, it takes power away from the technique, so that when you do actually want to use it for emphasis, it's impact is diminished. However, this can also be used to your advantage, for example, lets say you have a scene with your hero and the villain. They're bantering back and forth until the scene climaxes with villain saying "It was I, who killed your sister". Already, big, impactful information for the hero. So you can play it two ways, you can do what I described earlier and play that line on our hero's face to see the emotional impact, OR we can intentionally play the preceding dialogue in an overlapping fashion, then cut to the villain's for his "It was I, who killed your sister" line, and then cut to our hero for his/her reaction. So what does that accomplish? Well the previous overlaps reduce the importance/impact of the preceding dialogue, and so cutting to the villain for his line creates a strong impact on the viewing audience. Now, neither way is right or wrong, they're two different approaches to the same beat, but the point is to use overlaps in a deliberate fashion, not arbitrarily.
So this leads me back to the cut note and why it shows ignorance on the note giver's part. They don't really know what overlaps are for or how to use them to create emphasis in a scene, they just know they see them a lot in other shows, and therefore they should be more present in the one he/she's looking at now. When someone sits down to give notes on a cut, they are sitting down with the intention of finding things to criticize in the edit. That's just how it works. You'll always get dumb notes from people who only know what they're looking at doesn't conform to what they think everything is supposed to look like, it's just part of life as an editor. If they're sitting in a room with you, you can try and educate them but likely they're sitting in a office at the studio and your show is just one of 5 that he/she had to watch that day. If you have a strong director (or show-runner if your on a TV show), those kind of notes will likely either get filtered out or vetoed by them, but yes, they're still annoying when they do make it to you. :)