You might keep your money in a bank, but have you heard of a time bank? This online service allows users to trade
services with one
another without exchanging money. For example, a hairdresser gives
someone a haircut for one hour of credit in the time bank. The
hairdresser could then use that credit to have a plumber come work for
her for an hour. Time banks are useful for people who can't arrange
direct trades. The plumber might not want a haircut, but he can work
for the hairdresser and earn credit to use with someone else.

How does the detail "The plumber might not want a haircut, but he can work
for the hairdresser and earn credit to use with someone else" best support
the central idea that time banks are a convenient way to get things done?