If default Google Analytics tracking code is installed on pages with different domains, Analytics will count these users and sessions separately.

This statement is true. By default, Google Analytics uses the domain name to identify unique users and sessions. If the default tracking code is installed on pages across different domains (e.g., example.com and anothersite.com), Analytics will treat visitors to each domain as separate users and create separate sessions for them, even if it's the same person browsing both sites. This is because the default cookie scope is set to the domain where the tracking code is installed. To track users and sessions continuously across multiple related domains, you would need to implement cross-domain tracking.