AJAX and all related technologies such as Angular, Reactive and BackboneJS improve the quality of the web pages.
Imagine, if the request for a page is from a bot, then the server sends back a rendered page (by a 3rd party services), otherwise (if the user-agent is not a crawler then) everything goes as normal. This is what happens in a prerender system.
Prerendering is a service to render all data on a page in preparation for search engines to see it.
Prerender will intercept a request to see if the request is from a bot or a crawler then send the cached version of a page to show with all data, Images, etc. rendered before. This means that the prerendering process is only used for crawlers and bots only.
The effect of Prerender
Prerendering services are effective for SPAs where you are not worried about what a crawler sees.
To check the effect of the service we run a website with a SPA for a while and then add a prerender service to the site. As you can see, Google bots fine some pages but not all of them (in this case less than 10% of pages). See the following figure.
By adding prerender services, then Google bots find all pages and index them. Google bot finds 100% of the pages and indexes them. Remember then, these pages are not added in the site map (see the figure).
This is very important in Content marketing, as you can see in the following figure, the number of indexed pages increased, the impression is too.
This means you are seen in the search!!