A hood will block your peripheral vision IF you place it over your helmet.
If you place it UNDER your helmet and properly fasten the little strings, it will turn with your head and allow you to see fine. Additionally, hoods are thinner than hats or other head covers and fit under most helmets whereas hats do not (not in a way that allows the helmet to rest on your head as intended, anyway). When it's cold out and/or pouring, I wouldn't trade my hood for anything.