FPGAs just allow you to remove a layer or two of abstraction and corresponding latency (vs a CPU) where you don't want/can't have it and gives you control, speed and/or efficiency improvements in exchange. The price you pay is you're dealing with things at a much lower level (i.e. bits and wires)... if you don't need the trade-off, don't make it. They are for the situations where there is no off-the-shelf solution that quite solves your particular problem adequately.