I remember attending a talk by a US professor speaking on "plain language for lawyers" ( - an oxymoron, I hear you say). One of his examples was a set of fire instructions on the back of a hotel room door which concluded with the message "If you are deaf and/or dumb, please let reception know in advance so that appropriate arrangements can be made."

His point was; why the "and/or", why not simply "or"? Would someone otherwise read the sign and think "Oh it's OK I'm deaf AND dumb so I don't need to let the front desk know in advance"?!?!?