It's main aim is to provide rigidity to the plastic body of the cartridge. In the original van Alstine article it recommends use of epoxy to firmly glue the Longhorn to the cartridge body, as close as possible to the cantilever. Epoxy cures as a rigid plastic and helps to make the cartridge body more rigid and therefore reduce cartridge body vibration. At least that's how I've understood it. I could be totally wrong here.
The wings additionally provide lateral stabilisation.
For unipivot arms, I think a better place to place stabilising wings would be at the arm pivot, if possible a bit below the CoG. My arm is quite stable, but I've been thinking of trying stabilising wings to see if it brings improvement.
