I keep all my coffee grounds. I have a septic tank and I’m wary of throwing them into the pit!
But the main reason is we have very sandy soil out near the ocean and I want to add organic matter. Coffee grounds are generated in big quantities at my house and I’m gradually spreading them across all my growing patches. This has the double virtue of putting nitrogen into the dirt, and repelling slugs who hate the grounds. The caffeine is poisonous to them, but I entertain the fanciful notion that as some caffeine is absorbed they get hyper! Slugs as a rule don’t like gritty substances, and washed out and crushed egg shells are a useful protection when spread around sensitive plants like hostas and lilies along with the grounds. .