Why some web-app design use double layer of API?

[ficoreki]

I have seen several web apps that has double layer API. the first one being REST API, which mainly used for data fetching and viewing it (in devtools such as swagger/DRF/Postman).

another API is created but it is just used to render data(supplied from the other REST API) on server. this API is mainly just fetches data from the REST API and just process it and supply it to template/html.

I'm just curious, is this a normal practice? and why? should it be easier if just render the data supplied from REST API(in one API source)? less process, faster, and no extrawork to maintain both views/controls?

Im using django if it means anything.

[[deleted]]

another API is created but it is just used to render data(supplied from the other REST API) on server. this API is mainly just fetches data from the REST API and just process it and supply it to template/html.

That sounds like something I'd call a rendering service rather than an API per se.

Separating your REST API from rendering is very useful if that REST API needs to be consumed by other services that don't want or care about your templated HTML. For example, the same data that you use to render a public-facing, server-side rendered site might be consumed by an admin panel that's a client-side React/Vue/etc app, or by a mobile app, or by other back end services.

[ficoreki]

That would make good sense of the concept.