I've just made a fresh installation of slackware 14.
Till now, i used to add my user to several groups as described here
Now, when i created my user account, i only add myself to video and audio (for trying).
I'm surprised to be still able to, in desktop env, mount devices (i'm not member of plugdev), shutdown computer (i'm not member of power), manage network with NetworkManager (i'm not member of netdev), ...
I will do more tests in cli, but i wonder if there is a doc that explain the usage of each groups ?