In the Next.js docs, the section on useCache mentions that the useCache directive can be used alongside Partial Pre-Rendering:

If used alongside Partial Prerendering, segments that have use cache will be prerendered as part of the static HTML shell.

However, the section on Partial Pre-Rendering mentions nothing about needing to use useCache. In fact, that section, and the linked video, makes it sound like every component outside of a Suspense boundary automatically becomes static, i.e. pre-rendered, without the need for useCache.

Is useCache needed alongside partial pre-rendering, if so why?