Part of the conclusion p 214:
The First Fleet was a very expensive venture. ... the Pitt administration spend largely to make the New South Wales colony succees.The five sections of the book cover Planning a Convict Colony, Assembling the Fleet, Preparing to Sail, The Voyage and The Cost. This book is definitely worth reading by anyone interested in Australian history, but especially if you have convict ancestors.
It did so because it saw that a colony in the southwest Pacific Ocean would be clearly in the nation's interest, not only because it would provide a solution to a troubling penal problem, but also because it would acieve other objects - most immediately a base and a source of naval materails, and more generally as a point of interchange for an intended vast marketing network.