I'm curious as to what can be grabbed with the Advanced Grabbing Unit from the Asteroid Redirect Mission update. The wiki says that it can "pick up just about anything," but that's just not reassuring enough. Can it grab space debris from orbit? How large does the object have to be in order to be grabbed? Any videos of it?
The short answer is:
"Anything that does not have a Sphere of Influence"
Anything you have built and have launched or is sitting on the launchpad, asteroids, kerbals. You can use the claw to attach to these
You can't use the claw to attach to Duna or Mun or anything else like that
As per OP's request: video footage of it being used on something other than an Asteroid
They can grab onto other ships/stations/satellites as well. If you launched ships without docking ports that need rescuing/refueling, launch a refueling vessel with an Advanced Grabbing Unit, and it can latch onto the stranded ship and is then considered "docked" with the other ship, and can transfer fuel to it.