I'm not one to talk about camera system weight when traveling- I took a 5x7 camera plus tripod, six lenses, and a dozen film holders, plus a 35mm rangefinder with two lenses with me to Argentina. I could have gotten away with only three of those lenses for 85% of my shots, and probably gotten 95% (or equivalent images that I would have been just as happy with in the long run) with just two. But at the point you're hauling a view camera halfway around the world, what's a couple extra lenses? I've also taken the 5x12 to San Francisco before. But it's funny- I don't think I'd feel happy packing a 35mm camera with JUST a 50mm lens, but a 240mm on 5x7 is just fine as a sole optic. The more I work, the more I'm liking the idea of a single focal length prime lens as the one and only lens I've got, because it pushes my creativity and makes me think more about my composition.
If you're shooting in low light, those faster lenses pay off big time when it comes time to focus. I know I botched a night shot I was taking out in San Francisco because the lens' maximum aperture (this was on a 5x7) was f8. The shots I did with my f4.5 lens were much more accurately focused and stayed tack-sharp.