Resolution

Relatively to files storage location there are two types of Sitebuilder sites: published and non-published site.

Whole content of non-published site is stored on Parallels Plesk Sitebuilder server in site's directory /usr/local/sitebuilder/htdocs/sites/90/9045a6c768e89f9fa5ca2bb8a7c5b78c, where 9045a6c768e89f9fa5ca2bb8a7c5b78c is unique site identification.

Text content of site's pages is stored in Sitebuilder database. Images (custom banners and logo, images in Image Gallery, eShop and other modules) are stored on file system. Configuration of Sitebuilder modules in site is stored in SQLite database file located at /usr/local/sitebuilder/htdocs/sites/90/9045a6c768e89f9fa5ca2bb8a7c5b78c/data/storage/sb_modules.php.

When the site was published for first time all images from Image Gallery, eShop, other modules and SQLite database file are uploaded to publishing host via FTP. These objects are removed from Parallels Plesk Sitebuilder server. Site's content is taken from Sitebuilder database, compiled to files and uploaded to publishing location also. Site's text content and images that serve site's template configuration (custom banners, logo) remain on Parallels Plesk Sitebuilder server.

For published site configuration of modules is stored on publishing host, Parallels Plesk Sitebuilder server stores only text content of site's pages.

In this way when you open site in Wizard and edit modules, Parallels Plesk Sitebuilder communicates with publishing host. Modules configuration is taken from SQLite database, images are uploaded to publishing host immediately. It is not needed to publish the site to upload the modules on publishing host. 
If you plan to created a site with huge number of images it is recommended to publish the site first and then uploaded images one by one. For details refer to article: http://kb.parallels.com/en/5788.

Before site was published new images and changes are not shown on published site. There is a parameter that manages content of published site.

When site is published further only changes are updated, the site is not copied as a whole. To publish entire site content (with configuration files) it is required to enable option "Republish the entire site content" on page Publish in Sitebuilder Wizard.

Additional information

Publishing host is server with FTP and HTTP where Sitebuilder site is published to. It may be one of several physical servers.During site publishing files are uploaded via FTP, Parallels Plesk Sitebuilder queries published site via HTTP requests.

Additional information

For schema of Parallels Plesk Sitebuilder refer to article Installing Plesk Sitebuilder in Distributed Environment in Plesk Sitebuilder 4.5 for Linux/Unix Installation Guide.