I've seen it used for seniors who don't necessarily have a physical impairment or restriction, but rather a disease or illness like Alzheimer's. In such cases, the family of this passenger wants assured assistance from departure to arrival, and means that the passenger can travel alone.
Basically, the procedure is exactly the same as if it was a child traveling unaccompanied - the fee is paid, regular restrictions apply (such as often only for direct flights, cannot book last flight of the day). The same sort of info is also required - meeting party at the other end, phone contacts, and the meeting party will need to present i.d. confirming they are the person named on the form.
Using an airline's unaccompanied minor in this way often provides both the family and the passenger additional peace of mind - it does incur the UM fee but is often a good alternative to trying to secure other options such as a travel companion.
