default handling of new crm entity fields?

Hello - How does CRM handle new entity fields?  For example, if I open Contact in Customizations and add a new field does CRM automatically create a ContactExtensionBase table?

Does CRM follow this pattern for all entities?  For example, if I add a new field to SystemUser does CRM automatically create a new table named SystemUserExtensionBase?

I've noticed this pattern in the local CRM implementation I'm working on and I was wondering if this was a convention that the dev team implemented or if CRM implements this pattern by default based on changes made through its UI?