"A geisha is not technically a prostitute. Here is a useful rule: Anyone who is not technically a prostitute is a prostitute." That's Roger Ebert, summing up the role of a geisha for the film adaptation of Memoirs of a Geisha. We couldn't have said it better ourselves, so we won't try.
Geisha act like their job is to play guitar, dance, and pour sake, but these girls aren't selling tea in the teahouse. Here's the real T (i.e., the truth): they're selling sex. Sex sells, even in Kyoto in the 1930s.
Questions About Sexuality
So, are geisha like prostitutes? What is the difference between the geisha and the prostitutes in the book?
What parts of a geisha's rituals are sexual in nature? Why is sexuality such a major component in a geisha's life?
Why aren't geisha allowed to have sex lives outside the okiya?
Does Sayuri ever take control of her own sexuality? When? What are the results?
Chew on This
A geisha is basically a commodity to be bought and sold for entertainment, and sex factors into her currency.
A geisha's value lies in restricting her sexuality and offering it to only a few men. With too much supply there wouldn't be high demand.