I've never got on with tandems. I'm too much of a control freak to stoke (even with a captain I'd trust with my life), and not strong enough to hold the bike up to captain it.
There are a couple of exceptions - the Altena recumbent bike tandem, which I felt more comfortable on than perched on a saddle, and any recumbent tandem trike, which you simply can't fall off, unless you really try! Alas, the later requires a lot of money, and even more space! But what a machine. You think you get attention on a single recumbent, try riding with a tandem one!
I did find that on a regular tandem, I was more relaxed if I closed my eyes. And my companion found an odd psychological thing. If I put my hands on his back and pressed slightly, it felt like he was being pushed along, and it actually felt easier to him to pedal, despite it actually making no difference whatsoever....
For a couple who are both comfortable, I can see the benefits. I think it's especially good if the stoker is a less regular cyclist - their power is evened out, and they are less likely to fret over not having control.