I think there are two places where people say to use an impact wrench.
1) The bolts holding the rear strut to the wheel hub are a PITA to remove. I did mine without and had to use all sorts of levers, jacks, kicking at wrenches, etc to get them free, but it worked in the end.
2) The top bolts holding the strut into the top mounts. This is because the strut shaft can rotate and cause problems. I think it works fine if you loosen these bolts when the strut us still on the car.
So, you can certainly do them without.
More importantly, do you have spring compressors available? I've heard of people doing it without, but I used them.