Hi again, all generation occurs on the server side( i.e. with local files on the hosting ), before anything is sent to the user's browser.

So, once html is completely generated (with all content ) - it is sent to the user and browser therefore had only one request to get that page.
After parsing of html browser may send additional requests for external sources - images, scripts, css files etc. - this will have nothing to do with CMS, but your html design defines it. Also Couch can help embed( include ) all external sources into the resulting html, reducing requests to server( effective with css, js ) which is very effective as you also mentioned it. This is done with cms:embed tag.
http://docs.couchcms.com/tags-reference/embed.htmlAnd also CMS can convert images to base64 encoded variants, that are sent as text inside the html, again reducing total number of requests to server, since images are preloaded and browser is quick to decode them from a given string. More here
viewtopic.php?f=3&t=9663&p=25808&hilit=base64#p25808It is possible then to have only 1 request for a page, which is absolutely amazing in terms of speed( if images are small ).