Cerebrospinal fluid is a clear, colorless fluid found in the subarachnoid spaces in the cranial cavity, where it functions as a shock absorber for the delicate tissues of the brain, according to Fluids and Barriers of the CNS. Cerebrospinal fluid also removes waste in the absence of a lymphatic system.
Cerebrospinal fluid circulates throughout the central nervous system, where it performs a dual role. One benefit, according to About.com, is that the layer of fluid surrounding the brain is able to absorb shock and provide extra padding that helps protect the easily damaged tissues of the central nervous system. Another important benefit of cerebrospinal fluid is its role in maintaining a healthy circulation through the brain and spinal cord. Cerebrospinal fluid delivers nutrients to these areas and extracts waste in much the same way that blood does for other parts of the body. The free circulation of cerebrospinal fluid, therefore, is essential to keeping individual nerve cells healthy and removing toxic byproducts of normal cell metabolism.
A 2014 paper by Brinker et al., published in Fluids and Barriers of the CNS, suggests that cerebrospinal fluid might have yet another role in exchanging fluid with blood and interstitial fluid. The paper also suggests that cerebrospinal fluid circulation might play an important role in the brain's regeneration during sleep.