If you're talking about the two screws on the power side of the older white macbook, they do nothing.
I have the same MacBook the OP has, and I've disassembled mine entirely before. You could actually look up what model it is before taking a guess.
Also, it seems to me that the screws must do something or they wouldn't be there. Maybe they're not really necessary, but I can't imagine they do absolutely nothing. Even looking aesthetically pleasing is doing something
Well, I stand corrected.
Yes, please stop guessing and look up the model number!
I was, of course, looking at the front of the Mac and so the two screws on my left do what I said they did. Of course, looking at the back of the Mac (which makes far more sense) the left screws do nothing.
Or are you talking about the 2 screws that connect to the topcase and screen hinges on the rear of the MacBook ?