What are some of your learnings from migrating a large app to NextJS?

We're planning on migrating our fairly large codebase over to NextJS from Create React App next year and I'm keen to understand what we should be looking out for which might catch us off guard.

If you've embarked on a similar migration from CRA, another framework or a homegrown React app to NextJS what are some of the learnings you discovered along the way that would be useful for us and other teams to know before diving in?