Human slavery might be one of the few exceptions to this. People can reproduce and create more people provided they are given the bare necessities of life. As long as you could keep the enslaved under control, you would have new slaves you could constantly sell and they mostly took care of themselves.
Honestly it sounds like a great life for an unambitious, lazy person. Maybe we’ll all be able to experience something similar when humanoid robots are commonplace in the future. Find an isolated piece of land with a few robots. Make them grow food and commercial crops. Raise some animals. Live a life of relative self sufficiency and leisure.
Too capable (but also valuable!) slaves tend to be self sufficient and strong enough to throw you off.
Too weak (and therefore non-valuable!) slaves tend to be easy to control - but are a huge drain on the system, including ‘master’ management, which is often the most constrained resource anyway in any hierarchical system.