[p_l]

Anything where you wish you could have an ASIC but you don't have the budget for custom ASIC, and where using smaller chips either makes for worse Bill of Materials or takes up more space.

They are used everywhere, including some very small ones I've seen used purely for power sequencing on motherboards - usually very small FPGA with embedded memory that "boots" first on standby voltage and contains simple combinatoric logic that controls how other devices on motherboard are getting powered up faster than any MCU can do it - while taking less space than discrete components.

Glue logic, custom I/O systems (including high-end backplanes in complex systems), custom devices (often combined with "hard" components in the chip, like ARM CPUs in Zynq series FPGA), specialized filters that can be runtime updated.

Lots of uses.