Use of the past perfect tense (“I had eaten”) seems to be contentious among editors these days. It does require extra words and is therefore a little more complex for the reader to process. If overused, it makes prose cumbersome. But when your narrative is already written in the past tense–like most fiction–how do you represent actions that happened prior to the current scene? Sometimes, the simple past (“I ate”) will serve, but you have to judge it on a case-by-case basis. Personally, I use the past perfect freely, because it’s logical and my favorite authors use it.