There are a number of great reasons to consider a headless architecture for a web project. I sometimes hear site speed listed as a primary motivation. Is a headless website guaranteed to be faster? Let's explore this idea.
Allows a headless application to retrieve extra information for a page or path, that isn't included by default in the JSON:API representation of the content object: breadcrumbs, metatags, redirects, etc.
Provides an API endpoint for headless applications to send strings for translations or overrides, and another to retrieve all translated decoupled strings.
Adds a tab to nodes that allows a quick preview of the node's representation as JSON:API. If using this with a Chrome browser, the formatting can be improved using the JSONVue extension, with the option enabled to format contents in frames.
Traditionally headless sites have to use a specialized search service like Algolia. This module allows a headless application to query your Solr index through Drupal using JSON:API.
I also looked at SolREST, but I'm not sure I like the idea of bypassing Search API, or the fact that it only has a dev release as of this writing.