We are discussing weather or not one should have a neck lift at the same time as a face lift. In general these two structures are intimately related based on anatomy the soft tissue that covers the face also travels down into the neck.
Now, therefore these structures should be thought of as one continuous unit. The neck should always be evaluated and weather or not the neck is addressed at the time of the surgical procedure would be a decision made based on a specific patients anatomy and the plastic surgeon's opinion. In general, when people tend to have laxity of the mid and lower part of there face they often have laxity of the neck as well therefore in addition to making the incision around the ear and lifting up the lower and middle portion of the face a second incision is often made just under the chin where the entire neck can be accessed and the muscle that is in this area can be tightened. The skin is then re-draped and a small amount of skin is removed in order to make the neck as tight as possible. So in summary the face and the neck should be thought of and evaluated as one continuous structure.
And depending on a patients specific anatomy there one or both structures will be addressed during surgery.