I have used sheets of newspaper, covered with grass clippings. I found that after being soaked and dried a few times, the newspaper actually sheeted water away from the plants. Not good, and I had to punch holes in it.
Really kept the weeds down though. Nonexistent. Once I got a handle on the watering, it worked out ok. But the plan was still pretty dumb. What purpose did the grass clippings serve? None.
This year, I am keeping bags of shredded paper(old bills and such) on hand, and when I get grass clippings, I'm going to mix them 50/50 with the paper and use it as a mulch.
Hopefully the carbon will balance out the nitrogen in the grass, and as it decomposes, it will block weeds, let water through, any keep worms happy.