icloud: What are the limitations of DNS usage that an iPhone ignores?

So I have an iPhone with iCloud. Apparently, it has not been reported as stolen since it requires the login of iCloud after the start. I read that it could be "DNS skipped", but I also read elsewhere that there are "usage limitations", so the DNS procedure should be done every time you start the phone, I read somewhere else, if you download, AppStore will ask you to log in to previous iCloud. I could not find a definitive list, and it is confusing since the guide says that after the omission of DNS you can make calls, use WiFi, take pictures, etc. So, what are the limitations of using DNS when omitting an iPhone?

Thanks in advance