Depends if they're fresh or not - old coffee grounds shouldn't be used (they tend to ferment) but fresh ones, particularly if the beans were organic, can be useful, either on the compost heap in small amounts at a time, or spread round the borders, again, small amounts, though you can use larger amounts around acid loving shrubs. Some people use them as a slug and snail deterrent, but they just get washed away by the rain, so not that effective really. Link below to some info

http://conversation.which.co.uk/home-energy/coffee-good-fertiliser-compost-for-garden-plants/