How private is my Apple ID?

I would like to know how private my Apple ID is. Does my Apple ID have its own unique account identifier like a MAC address, if so do apps I download know that identification serial number? If apps do, does changing the email change the unique address or does it stay the same?

So for example. If someone was to be banned on Twitter or YouTube or any other app. If they was to get a new phone but have the same Apple ID would the company in question identify the person who was previously banned because of their Apple ID?

I am curious to know how extensive online Identification and tracking has become. Apple bark about how they value their customers privacy so I want to I know how honest that statement is.

Thanks people in advance.