Meditation helps in reducing mental clutter. If you are meditating you are dismissing many worries and concerns as not being all that significant, like 99% of smallish things we worry about.
Then getting rid of physical clutter will seem logical too, as a consequence. A lot of papers and small insignificant objects that need to be thrown away.
Time clutter is checking emails, bank balances, Facebook statuses, or stock prices too often.
There is productive, creative clutter as well. But reducing the non-productive clutter will help here too. If you are creative you won't have to worry about being too neat, because some of the clutter will follow you around anyway. I always have stacks of books following me everywhere I go: in my car, office, apartment.