It always seems like something they added just for the sake of adding it than because it had to be part of the story they were trying to tell. The only series where it made sense was as you said Tanya where it was an intetional part of the punishment by Being X and it even then has no real impact on the plot or the character. 99.9% of the time gender bender bullshit serves zero purpose and is just there because someone in the writing team has some weird feitsh for it.