When to write a LOCI?

When are you guys writing your LOCI’s? Right when you get waitlisted? Or are you waiting? I’m also not sure what I’d put in mine lol. I already did “why x” for most of my schools and there haven’t really been any new developments in terms of my resume and things I would want them to know lol. I get I’m just supposed to reiterate my interest but I’m not sure what else to add…