I think it's more the legality mate, no idea on the actual ins and outs as different people will tell you different things. My GTI has them anyway so if I fit auto levelers, I know I'll have an OEM factory fit headlamp system. That way, any insurance/police implications mean I'm in the green.
The actual washers themselves don't do a tremendous amount. I remember the old Volvo 850's used to have a washer arm on either side so it could scrape away the crap after the jets had fired. Old skool!
Where are these split rim pics?