Shave the sucker. When you shave the rest of the truck (everything)- having that smooth transition from roof to sides just looks clean. If you do shave other parts and leave the drip rail, IMO, it looks unfinished.
It will take a bit of time to do, and you must be patient - but I think it is one of the best mods that can be done to these old trucks.
As for it having a purpose - well I guess you could just avoid driving it in the rain!!!!
- Ryan