In a report from MacRumors, it has been noticed that users who upgrade to iOS 11 or macOS High Sierra will automatically be migrated to the 2FA system if they weren’t already using it. In an email Apple has been sending to users, “If you install the iOS 11 or macOS High Sierra public betas this summer and meet the basic requirements, your Apple ID will be automatically updated to use two-factor authentication.”
Prior to this there was the two-step verification method which sent a code to a trusted number, while 2FA sends a code to all registered trusted devices. It will also show users a map and an approximation of where the requested sign-in is taking place in the event someone from another city or country is trying to hack your account. However apart from that difference, both systems are more or less identical.
This shouldn’t really change the way that iOS and macOS users use their devices, so for the most part this change shouldn’t really disrupt your overall experience.