I guess everyone knows what a good mice catchers cats are. It's a known fact that they catch mice! They may play with them or they may not. Whether they eat them or not, it does not matter.
Mice have a funny way of finding their way into our homes. They find an opening somewhere. But they are goners as soon as my cats sense their presence.
What amuses me about my indoor cats, however, is how they manage to take care of flies. They have replaced my fly swatter. Once these cats catch sight of a fly, they run from window to window in hot pursuit. Across the room they chase the pesky insect. They run and jump until there is a fly no more. They eat it!
Who says cats are not useful pets? My cats solve both the mouse problem AND the fly problem. I'd say they earn their keep.