Community Builder does not need the Joomlapolis server for running.
The only uses are:
1. In admin panel and configuration for checking and displaying if there is an updeate, as you noticed, and
2. if you go to Plugin Management / Install and Update, and then go to the "Install from web" tab to install add-ons or updates directly from Joomlapolis.
You can turn on or off any or all of those in CB Configuration / Integrations and set the interval of checking, and you can set a site key (that you can get from your user profile on Joomlapolis) for installation and update of professional/developer add-ons:
- Version Checking
- Plugin Version and Build Release Checking
- Install from Web
- Install from Web Site Key
The CB Configuration is stored in the database, so no file needs to be writable for configuring CB.