Do you need a radiator fan shroud?

No, if you want your car to just run. Yes, if you want your car to perform. I wouldn't say its a dramatic difference, because all the shroud does it regulate the air the fan is blowing. This cools the engine. I've seen people run without it, its not too uncommon. Might was well change it out. But if its an old car and not modified, it really doesn't matter