Son started playing cello this school year (3rd grade). A couple of weeks ago, I dug out my guitar, and started playing chords to his practising. To the surprise of both of us, it's been a lot of fun for us both. He says "it sounds more like a real song", and has gotten slightly annoyed with me on a couple of occasions when I goofed up and had us start over. For me, it gives me a real live reason to play, and of course is a welcome chance to do something with Son.
And for both of us, it's been a great help with our timing. Son would be all over the map, tempo-wise, paying much more attention to the notes rather than the timing; now, he does a great job of keeping time, and enjoys counting off to start ("1, 2, 3, 4", or "1, 4, hut, hike" or sillier).
Big, big win.