The 259th prohibition is that we are forbidden from giving a Jewish servant unnecessary work. Such work is called avodas perech.
The source of this prohibition is G‑d's statement1 (exalted be He), "Do not rule over him with unnecessary work."
Only when we need a certain job done may we give it to him. In the words of the Sifra: "The verse 'Do not rule over him with unnecessary work' means that you may not tell him to warm up a drink when you don't need it." The same applies to similar cases. Our Sages merely brought an example from one of the easiest and simplest types of work in order to teach you that even it is prohibited unless it is needed.