Grass Clippings

This is one of the most abundantly and easily available mulch materials across the country. It provides nitrogen to the soil, if incorporated fresh. However, application of green grass in rainy season may result into the development of its own root system which will be detrimental to plant growth. Therefore, use of dry grass as mulch material is suggested.

Benefits

The benefits of using fresh grass clippings as mulch include cooling the root zone, conserving moisture and adding back up to 25 % of the nutrients that growth removes from soil. Mulching with grass clippings has the added benefit of taking one more step out of an already drudgery filled garden chore.
Turf grass clippings contain high amounts of nitrogen, a macro-nutrient that all plants need to grow and flourish. Can I use grass clippings in my garden? This is one of the best ways to use the refuse and the clippings break down quickly and add nitrogen to the soil while increasing porosity and reducing evaporation. You can use fresh or dried grass clippings as mulch.

Source:

http://www.gardeningknowhow.com/garden-how-to/mulch/mulching-with-grass-clippings.htm