In new Apple computers with its custom T2 chip (currently the iMac Pro and MacBook Pro 2018 models) it serves the purpose of "the System Management Controller, image signal processor, audio controller, and SSD controller." That means it can handle the system's secure boot system and on the fly encryption, as well as image processing for the FaceTime camera. While the enhanced security is nice, it has additional implications.
According to MacRumors and shown on documents posted by Motherboard, anyone doing significant repair work on these systems will be left with a nonfunctioning system until they run the "Apple Service Toolkit 2" diagnostic software. For the MacBook Pro that includes "display assembly, logic board, top case (the keyboard, touchpad, and internal housing), and Touch ID board," and on the iMac Pro, it's the logic board or SSD.