I've had great success using large amounts of coffee grounds as an ingredient in my sheet mulching. Whenever I'm ready to start a new bed at my home or for a client, I use a thick layer of horse manure (8 inches or so) covered by two layers of cardboard. I follow that with a couple of inches of coffee grounds, some compost and amendments, then a thin layer of wood chip mulch.
The coffee grounds accomplish a few things: 1. they are a good addition of nitrogen right on top of the carbon-rich cardboard, 2. they cover up the manure smell completely with a nice fresh coffee scent, and 3. they hold an ideal amount of moisture. Whenever I get ready to plant annual crops into these beds I just dig down to the top of the cardboard, adding a little soil and tucking the coffee grounds and mulch back right on top. I'm amazed at how well this combination holds water--when I return days later to add more plants it often needs no additional irrigation.
I can see that the plants are loving it, too. They already grow like weeds in the first month or two, even though sheet mulching is often recommended to do months ahead of planting time.
