This is underdiscussed IMHO. I refer to the render function calls as "the way down" and then after everything is mounted when React starts calling the useEffect

This is underdiscussed IMHO. I refer to the render function calls as "the way down" and then after everything is mounted when React starts calling the useEffect callbacks "the way up". Many applications suffer from the waterfall rendering problem but even for those that don't, if they are large, they will absolutely want to kick off network calls on "the way down". You can easily add a ton of time to LCP by waiting to kick network calls off until the tree has mounted. I actually go a little out of my way to make sure as much of the tree as possible can render and mount with missing data. This way the work is occurring while data is fetching in parallel, and then a minimized number of components need to be updated once the data has arrived.