I've read many places that it is hard to find out where the Swiss Pass quits working for the full fare as you go up into the mountains. We were just there and were told by the ticket agent that Murren and Wengen are the last stops out of Lauterbrunnen. After that, you will have to pay half price.
Having the pass was wonderful not just as a money savings but as a time and stress saver. You will be getting on and off many modes of transportation. A lot of time you will take 2 or 3 to get to your destination. It is so nice to just be able to show your pass. Most of them are synchronized so you don't have a lot of time from the time you get off one until the next one leaves.