They may be good for the plants, but definitely not for the drain pipes. Coffee grounds are one of the worst offenders for causing drain blockages since they are not completely water-soluble; and when they mix with kitchen FOG, they increase the risk for clogs.
One of the most common wastes in the kitchen, eggshells contribute greatly towards increasing granular wastes. Not only are they hard on disposable blades when they wrap around the grinding device, ground egg shells easily compound other blockages. Make good use of this kitchen waste (and coffee grounds for that matter) by transforming it into compost.
FATS, OILS, and GREASE (FOG)
The most common culprit and probably what most of us might think as the only cause for drain clogs, FOG includes not only fats, oils, and grease, but also dairy products like cheese, ice cream, milk and butter. Even vegan nut butter is not spared. Salad dressings, sauces, and mayonnaise, which include oil in their mixture, also belong to this group. FOG builds up fast and creates water-resistant barriers, so be more conscious when disposing them.