BAR have adopted the wavy lip along the side of the front wing endplates (I can see a mix up in our naming here). This design was brought out by Ben Agathangelou at Renault and subsequently Jaguar. Since then most teams have adopted it. The lower edge of the front wing endplate (FWEP) usually extends sideways to meet the maximum permitted width, the flat lip serves to act as a splitter to keep higher pressure spilling under the endplate to the underside of the front wing. I’m not sure how wave added to the recent batch of FWEPs works, As the channel formed is usually consistent along itself I doubt it is creating a vortex or unusual flow condition from its rear end (Although Ferrari and Renault have shaped this channel into a venturi). SO All I can offer as to a suggestion right now is that the curve adds surface area to the lip and hence acts to deters even more air passing under the endplate.
