In Chapter 4 of Guns, Germs, and Steel, what are the economic benefits of domesticating such things as cotton, flax, and hemp?

In Chapter 4, Diamond is explaining why farming was
beneficial to people and societies.  He, of course, mentions the food value of various
plants and animals.  However, he then goes on (on page 90 and beyond in the paperback
edition of the book) to talk about ways that plants can have economic benefits beyond
their value as food.

The types of plants that you mention
here are all good for the fact that they contain fibers that can be made into thread. 
The threads made from cotton and flax (which is made into linen) can be made into cloth
that can be used to clothe people.  Hemp can be used to make ropes and string to bind
things together.  In societies that previously had to rely on animal products for
clothing and for binding, these would have been very economically
beneficial.