It's usually used for anything software you need and the FPGA gets used for any domain specific circuit for signal processing and what not in hardware. The ARM core usually runs a linux or any other OS and is used for communication with other devices. It's just able to run at a higher frequency than most soft-cores, because it's a fully integrated and optimized circuit. So in theory that's a nice thing and gives you more space for custom circuits on the programmable logic part.
PS: The latest polarfire chips from Microchip use a RISC-V CPU. Since AMD has announced the microblaze-v (their proprietary soft-core CPU with RISC-V ISA), I assume they soon (tm) will release their zynq range with dedicated RISC-V in near future, too. But even if it's an open instruction set, it's still a closed source CPU
It's usually used for anything software you need and the FPGA gets used for any domain specific circuit for signal processing and what not in hardware. The ARM core usually runs a linux or any other OS and is used for communication with other devices. It's just able to run at a higher frequency than most soft-cores, because it's a fully integrated and optimized circuit. So in theory that's a nice thing and gives you more space for custom circuits on the programmable logic part.
PS: The latest polarfire chips from Microchip use a RISC-V CPU. Since AMD has announced the microblaze-v (their proprietary soft-core CPU with RISC-V ISA), I assume they soon (tm) will release their zynq range with dedicated RISC-V in near future, too. But even if it's an open instruction set, it's still a closed source CPU