Most of my light shield customers buy them for the starting line, to prevent red lights , the shield gives you a bit more roll-out, and of course with cars with no nose, the front wheels will click the ET stop.
But keep in mind the start line light beems are on the track [lower] and the finish lights are about 3" above the track.
For years we did not run a light shield on our JF car with 18" wheels with low profile tires , 2.00x18, but the rims had a lip , like Akront or Borrani , and we had no issues of red lighting, UNTIL we raced at a Heritage race in Phoenix, where we had a redlight for the 1'st time . When I checked the other JF teams they also had red lights with the cars that did not have light shields , but no red lights with the cars that had light shields. So yes we have been running a light shield since.
When I get a call for light shields I ask if they are having red lights because the front end is jerking the front end up at the hit, if so just add another 20 lbs on the nose, because a light shield will not help if the wheels are pulling out of the start line lights.
I hope this helps,
Jon