Transgender is also has the problems of implying that you are changing your gender rather than just saying society (and perhaps yourself) were wrong about their initial guess at your gender. Regardless Meanwhile, using transsexual can imply it has something to do with sexual orientation even if you mean your are changing your sex to better match your gender (and the type of people who want to emphasize that tend to be transmeds, poisoning the term enough that I wouldn't personally use it).

Transfem is useful for indicating you are trans in a way that is more in the direct of woman without necessarily being a woman; it intentionally avoids giving a specific gender identity, but instead rules out one. There are certain experiences that are much more common among transfem people than non-transfem people, so its a useful word for indicating whom a meme or question might be most relevant to without unnecessarily excluding NBs whom they are relevant to.