I have heard this one before and it's a great question.
Our apparatus has a 6" x 6" quarts light mounted on each side of the tip about 18" back from the last rung. They only times that they have gotten in the way for myself is when I've had to shoot through tree branches. the get tilted/pointed the wrong way or just collect leaves and small twigs. With 18" of setback, they are not close enough to the tip to be a problem when taking out an upper floor window for ventilation.
I actually appreciate them on there for the purpose of ventilation - they light up a pretty big area of the roof which can be especially helpful when first making access to the roof (especially flat roof operations)
If they are angle down while the aerial is bedded, they help to guage depth perception when the tip is approaching the parapit. When the beam of light goes froma 30' diameter to about a 2' diameter.........you are there or about to come in contact. At the turntable this can be very helpful when positioning the tip.
We run a fair amount of MVC's (car accidents) and I can hit the lights off of the onboard generator and it helps to illuminate the scene even though the ladder is obviously cradled. These two with the additional side mounted lights on the body, turn night into day.
All in all, I don't mind them, and if spec'd and mounted correctly, can really help in "most" operations.