Zak Greant relates the development of this exception in terms as a mother giving birth to her child. In fact, this child is a “savior” of sorts for those building an application under a FOSS license other than the GPL and wishing to include the MySQL Client libraries. It means that there is no longer a need to use the GPL on the overall application (as was the rule previous to this exception).
This is somewhat the reverse of a situation I spoke of earlier where you may include a GPL exception to include non-GPL libraries in an application. In this case, you would be including GPL libraries in a non-GPL application.