It targets mid-density glue logic, video bridging, motor-control co-processing, and communications protocol handling where you need more fabric than a CPLD but don't want the power bill of a Stratix or Arria. The 3981312 bits of embedded block RAM handle line buffers, small FIFOs, or distributed lookup tables without chewing up logic cells.
That means Intel is still manufacturing it, no last-time-buy notice has been issued, and you can plan multi-year production runs without an obsolescence-driven redesign. For a mid-density FPGA that's been in the field since the early 2010s, that's a solid sourcing position — the Cyclone IV family has long legs in industrial and communications equipment.
280 I/O — interface planning
280 I/O on a 484-ball BGA. The remaining balls are power, ground, configuration, and clock inputs.