Religionists insist (at least the vast majority of them do) that the Earth and the rest of the universe were specifically designed to nurture and entertain humans.
But that seems absurdly weird. After all, there is very little in the universe itself that is habitable (far less than a few trillionths of a percentage of its volume), and even on Earth, most of the planet is inhospitable to human life without tremendous technological attempts to modify either the planet or ourselves.
So, given all that, and yet for the sake of argument accepting the religionist premise that the universe is designed -- what could it be for?
Well, it's clear that carbon-based life isn't it -- too much of the vastness of the universe is hostile to the existence of such things. And if you are only considering a single species, well now the possibility is just idiotic.
But there is one thing that a superdesigner might have use for in making our universe -- supermassive black holes.
Think about it -- according to cosmology and physics, the formation of supermassive black holes (at least a few hundred-thousand times heavier than our sun) is fairly commonplace (one exists at the heart of the Milky Way and every other galaxy, for instance), and the energy potential of such constructs is tremendous. Think about it -- E=MC^2. A black hole with the energy potential of our sun would fit into a space about 3 kilometers (two miles) across. This would be a very convienent way to store and transport potential energy sources, wouldn't it?
On top of that, because of the tremendous gravitational and quantum effects that occur in black holes, it is possible that near the singularity within the black hole, a breach or tear in the fabric of our spacetime into another universe could be created, where the energy of the black hole could be tapped. Granted, we don't know if this is true -- but it's no more fanciful than thinking some magical sky fairy listens to our every wish and grants our every prayer.
If the universe is designed for black holes, not humans -- where does that leave us? Obviously, we aren't too important -- a black hole the mass of the earth would only be a few millimeters across, hardly worth mentioning! In fact, I would bet that if there were a "designer" of the universe, life on a small rock orbiting a second tier star in the backwater subdistrict of a minor galaxy wouldn't even register as a blip on their screens.
We're just the spandrel waste of the universe, and I for don't regret it for an instant. If nothing else, this possibility gives me the hope that someday, humans might just figure out how to harness the knowledge and power of such a designer, and make our own black holes (of course, the LHC might just do that before we're ready).