What do you mean by "you". Maybe "you" as in a general consumer don't need an FPGA, but I guess one could argue a general consumer doesn't need a general purpose computer either.

There are certainly many use cases where you absolutely do need an FPGA, i.e. anything were you need to process large amount of IO in realtime. For example the guys from simulavr (talk about how they use an FPGA for display correction) here: https://simulavr.com/blog/testing-ar-mode-image-processing/

Many modern devices would not function without FPGAs