It also a search to find subjects for portraiture which are visually strong.
Richard Avedon said that what he looked for in a portrait subject was "Someone who held a wall" which meant he looked for subjects that were visually and emotionally strong, subjects that would hold the viewers eye in the gallery or museum. They could not leave, they had to stare and think and stare some more. A strong visual subject could draw and hold the viewer.
I think part of my reason for shooting ladyboys is a curiosity into who they are, the other part is trying to find subjects that I am in interested in and that will hold the wall.