Fighting crime isn't the only way the Flash is able to keep the DC Universe safe. Apparently all of the Fastest Man Alive's running is crucial to keeping the enigmatic Speed Force from destroying the fabric of space and time.
When Barry Allen was first graced by the strange and powerful Speed Force, he used his speed for one thing and one thing only: to help people. Barry had long been an advocate for justice, ever since his father was wrongly accused of murdering Barry's mother. And while that strong desire led him to a career in forensic science, being the Flash allowed Barry to truly help those in need. Since lightning struck a chemically-doused Barry Allen, he's been running as fast as his legs can carry him and he hasn't stopped running as long as the Flash had his connection to the Speed Force.
And it's a good thing Barry has kept up the pace, because if he hadn't, the DC Universe might be in serious trouble. In the Flash #8 by Francis Manapul and Brian Buccellato, the Flash has entered the Speed Force in pursuit of Iris West as several others were sucked into a wormhole Barry think he's caused using his speed powers as Flash. While trapped in the Speed Force, Barry meets a man named Turbine, an old World War II fighter pilot who fell into a wormhole similar to the ones that have been plaguing the Flash. Turbine implores Barry to send him home, but Barry wants to learn more about the Speed Force and why he's causing wormholes to appear. Turbine reveals to the Flash that he isn't causing the wormholes, he's actually helping stabilize the Speed Force as it builds up energy while moving through time.
While much of the Speed Force isn't understood, this is an interesting revelation nonetheless. Flash and the Speed Force have an interesting relationship. The accident that turned Barry into the Flash is sometimes portrayed as an intentional event, with the Speed Force 'choosing' Allen to be its personal avatar. The idea that the force needs a "release valve" seems to back up this idea. But what's really intriguing is that this means the Flash is actually saving the universe every time he engages his powers.
One of the most tragic things many heroes have to grapple with is few ever know if they’re ever making an impact. For every galactic conqueror Superman stops, more rise in their place. Batman’s mission to save Gotham seems eternally stymied by the rotating case of colorful criminals plaguing Gotham. But Flash doesn't ever have to worry about that. His mere act of running keeps the DC Universe from going completely out of whack. Sure, Barry also keeps the world safe with the powers granted from the Speed Force but simply being a conduit for the Speed Force makes sure that the mysterious energy doesn't destroy everything else. Thanks to the Flash, every time he runs, the DC Universe gets a little bit safer.