Details of the WB-57F mission on the recent Shuttle launch:
http://www.nasa.gov/returntoflight/l...chasejets.html
Video which it shot on this page:
http://www.nasa.gov/returntoflight/crew/index.html
One is left to conclude that they used it "because they could" rather than for much practical value - short of having a ringside seat should the Shuttle explode.