Hi,
I think it's a combination of factors. It could simply be a redundant feature that got stuck in the paperwork which was approved for the 'P08' design and was retained as a result (the blueprints say that those funny extensions should go there, so we will put them there...).
I think it helps to keep in the grease and keep out the dirt. Remember that these pistols were not designed around modern lubricants, but they were greased up using products like vaseline. Sticky crud.
Swiss lugers in .30 luger are as accurate as they get, without these little extensions, so I doubt that accuracy had anything to do with it.
My favorite reason will be: it was on the prototype, so it went into the drawings, so it was approved by the German army, so it stayed.