Originally called S+7, invented as part of the OuLiPo (OUvroir à la LIterature POtentielle which could be translated into English as WOrkshop for POtential LIterature, WOPOLI).
I would kindly refer anyone interested -- to the works of Raymond Russel that really started the whole thing. Also, I would recommend the book of Foucault dedicated to his work (only one of this kind in his oeuvre), called Death and The Labyrinth (in English translation).
The Raymond Queneau Exercises in Style is a delightful introduction to OuLiPo. It takes the same story and tells it in 99 different ways (including N+7).
To me, a lot of what the OuLiPo constraints do is to free one’s writing voice from the worn routes that it might take without intervention. Doing an N+7 transpose on a text can open up new way of looking at that text since the nouns have been arbitrarily replaced and you see how the verbs and other auxiliaries work in the writing. My writing often has a subtle undercurrent of OuLiPo happening in it (e.g., the novel I’m revising started with a vague notion of story and 29 chapter titles taken from the Passover Haggadah. A similar shorter piece I wrote, “The Norton Anthology of Self-Destructive Behaviors” [https://uploads.documents.cimpress.io/v1/uploads/151c2c51-d2...], began with a list of self-destructive behaviors and a story emerged from those).