The printer will need to be free-floating and controlled separately. But once in optical distance of a surface, a control system similar to an optical mouse can keep the hot end still with great precision.

As for power, some high-efficiency solar cells on top can power the hot end.

As for need, one might be: Printing a camera mount on top of a crashed plane, to survey the area, or printing a mount for a radio beacon on an un-climbable part of a cliff.