We've had to do the 2-hr developmental visual skills test twice - between two different states. My son was born with visual deficits though and some other physical issues which affected his eye-hand coordination, attention, motor skills, etc.
My son was quite young when he had the first visual skills assessment and started vision therapy. He was in vision therapy from 3.5 to 6 yrs old with another optometrist from the school of optometry who performed the initial test.
We had our son re-evaluated last yr when he was 8. In fact, one of Dr. Silverman's friends and colleague recommended we have our son re-evaluated. Last year, the test was a bit different than the first time since my son was much older and was able to be assessed at a different level than when he was 3. Last year, she did a lot of rotating images, sequencing block patterns, reading at various levels, and some motor control stuff.
I'll say that I would not have had my son's visual deficits pinpointed more without the visual skills assessment performed last year. It can help enormously depending on the child and case.