What exactly does ておく mean in 食べておく?


The context for this question is from a conversation text. (みんなの日本語中級I第４課）The
speaker is leaving a voice message:

> ……今日ね、急な仕事が入っちゃって、遅くなりそうなの。晩ご飯、先に食べ **といて** 。じゃね。

といて here is just short for ておいて, but what exactly does ておく mean in 食べといて? Does
it in some sense imply preparing for something? What (nuanced) difference does
it make if the speaker said 「先に食べて」instead of 「先に食べといて」?

