Are these things really necessary? I am getting some RE 4.5" springs for my YJ. I have about 3.5" lift right now and its fine.

Is that extra inch really going to cause me problems?

It all depends on what you consider fine, the drop pitman arm is meant to get your draglink a little closer to level to eliminate most bumpsteer, yeah, you could lift your Jeep 20" and still not need a dropped pitman, you'd only be able to turn a little in each direction, if the draglink even reached, and everytime you hit a bump, the wheel would rip out of your hand. Ideally, your drag link should be as flat as possible, and parallel to your trac bar, if you still have one.

It basically all amounts to whether it is a street vehicle or a trail vehicle. If you use it on the street you should get one...if it is strictly a trail vehicle you really don't need it. As far as it affecting your steering capibility, for that amount of lift you probably won't really see a decrease in turnability. However, they don't cost that much so if you want it to work as it is supposed to buy one.