Coffee grounds decompose fine, it kinda depends on your soil. Coffee grounds are worm candy, it does draw predators to feast on my huge earthworms that are only there for the grounds. Inside a pot would be negligible as worms aren't good in containers. They don't have enough of the mulch to feed on in a pot, so their backup food resource becomes your plants roots. Kinda like pillbugs...decomposing matter is their need, but anything in a pinch becomes food when you do your job too well. Container pots are picky about their soils usually, less is better.
