Add note about NEXT_DATA hydration

docs/api-reference/data-fetching/get-initial-props.md

@@ -68,6 +68,8 @@ For the initial page load, `getInitialProps` will run on the server only. `getIn
 - `getInitialProps` can **not** be used in children components, only in the default export of every page
 - If you are using server-side only modules inside `getInitialProps`, make sure to [import them properly](https://arunoda.me/blog/ssr-and-server-only-modules), otherwise it'll slow down your app
 
+> Note that irrespective of rendering type, any `props` will be passed to the page component and can be viewed on the client-side in the initial HTML. This is to allow the page to be [hydrated](https://reactjs.org/docs/react-dom.html#hydrate) correctly. Make sure that you don't pass any sensitive information that shouldn't be available on the client in `props`.
+
 ## TypeScript
 
 If you're using TypeScript, you can use the `NextPage` type for function components:

docs/basic-features/data-fetching/get-server-side-props.md

@@ -14,6 +14,8 @@ export async function getServerSideProps(context) {
 }
 ```
 
+> Note that irrespective of rendering type, any `props` will be passed to the page component and can be viewed on the client-side in the initial HTML. This is to allow the page to be [hydrated](https://reactjs.org/docs/react-dom.html#hydrate) correctly. Make sure that you don't pass any sensitive information that shouldn't be available on the client in `props`.
+
 ## When does getServerSideProps run
 
 `getServerSideProps` only runs on server-side and never runs on the browser. If a page uses `getServerSideProps`, then:

docs/basic-features/data-fetching/get-static-props.md

@@ -14,6 +14,8 @@ export async function getStaticProps(context) {
 }
 ```
 
+> Note that irrespective of rendering type, any `props` will be passed to the page component and can be viewed on the client-side in the initial HTML. This is to allow the page to be [hydrated](https://reactjs.org/docs/react-dom.html#hydrate) correctly. Make sure that you don't pass any sensitive information that shouldn't be available on the client in `props`.
+
 ## When should I use getStaticProps?
 
 You should use `getStaticProps` if: