There are many reasons that a person should not ignore the differences between men and women when choosing another person of the same sex in one context and a person of a different sex in another context.
I will give two examples. When an adult man mentions that he is seeing a therapist, I ask, "Oh, that's nice, how old is he?" If the man tells me, oh, it's a woman and the man is your garden-variety heterosexual man, then I ask him whether that's a good idea.
I tell him this:
1. There is no bleeping way the woman therapist knows the trials and tribulations of having a penis. You might think, what if he's not there for sexual issues? On the slim chance that there's no issue there, I then go to #2.
2. Many men are quite skilled at getting women to "mother" them. Some make entire lifestyles out it.
3. There must be no chance the the therapist will become sexually attracted to you the patient. Some people don't have to worry about that, though they may be surprised.
Now, if you take these considerations into a sponsor/sponsee relationship in one of the 12-step, self-help program, Alcoholics Anonymous, for example, then these considerations become a matter of life or death. The differences between men and women become essential and "the men stick with the men", the "woman stick with the woman." The homosexuals and bisexuals have different issues. What's prudent is that a male doesn't get a bisexual or homosexual sponsor; similarly for woman.