Boost already is a very useful general purpose library. If you use C++ without boost, the need for something that is already provided by it will soon arise. However, boost is not perfect (and fcppt isn't either). The need for something that isn't provided by boost might arise, too, and there are even some things I consider not done "well" in boost. Freundlich's C++ toolkit (from now on shortened to fcppt) tries to fill in some gaps left by boost and even implements some replacements for a few boost components.
