What is the purpose of built-in FPGA with Intels new chip
But what is it for?


It's a bit early to say for sure. As of May 2018, Intel has only demonstrated one FPGA/CPU part (the Xeon Scalable Processor 6138P), and it's not yet shipping to the general public.

That all being said, the theoretical advantage of having an FPGA in the CPU package is high-speed, low-latency data transfers between the CPU and FPGA fabric (and, potentially, to connected devices). One of Intel's example applications is software-defined network switching, for instance.