A SiteAccess is a set of configuration settings that the application uses when you access the site through a specific address. When the user visits the site, the system analyzes the URI and compares it to rules specified in the configuration. If it finds a set of fitting rules, this SiteAccess is used.
Each SiteAccess can have different:
Many other settings in the application are also configured per SiteAccess (also known as "SiteAccess-aware").
When possible, always use semantic (SiteAccess-aware) configuration. Manually editing internal settings is possible, but at your own risk, as unexpected behavior can occur.