The Swedish author Sven Lindqvist travels through Africa in Exterminate All the Brutes, writing about the European colonization of the continent in the nineteenth century. He brings along a copy of Joseph Conrad's Heart of Darkness, which gives the book its title. The book combines personal memoir with a historical look at the legacy of colonization. Lindqvist starts writing in Tademait, which he describes as the "deadest areas of the Sahara."
I think his purpose in writing from a desert is twofold. On one hand, he is returning to the scene of the crime, so to speak. Lindqvist clearly thinks his book will be stronger if it is not merely a history, but, rather, a personal, subjective look at the horrors of the nineteenth century. It strengthens his argument, because he is not simply writing as an academic or a historian but as someone trying to understand, even participate in, what he is writing about. It also helps him get close to Conrad's book, as Conrad spent time in the Congo and drew on his own experiences for his famous book.
As a writer, Lindqvist would no doubt be aware of the symbolic value and import of writing from a desert. It can mean a place where there is no life and nothing grows. In a way, the Europeans, by destroying the culture and way of life that were there, by importing their own ideas, namely Christianity, and by exploiting the country, they made it into a desert. This recalls Tacitus's line "They made a desert and called it peace." The book is also about genocide, and the desert or wasteland could be the end point of such violence.