Sometimes a d-u will identify one or a few packages that can be removed by "autoremove", and it is safe to do so. But you always have to look carefully -- you can check with "apt-cache rdepends" and see if a package really has no other package depending on it. Today, on an LXDE netbook, it is showing me 11 packages, and some of them like xulrunner-23.0 clearly should not be removed, so it's not a day to run "autoremove".