The basic concept of the SNS stroller is that it is a "regular" stroller for your baby/toddler, but also allows bigger kids a way to ride along. It's not as bulky as a double stroller, and makes it easy for big kids to alternate between walking, sitting, and standing while riding.
Most of the time, big kids will want to walk. But, big kids do get tired and need a rest, so they can chill on the bench, have a drink of water, and talk to Momma. But they also want to see the world! So, even if they are too tired to walk (or it is to crowded/unsafe to let them walk) they can stand and see everything!
When you are 2 kids of different ages, especially when both are young, this is a great solution. When I was a mother's helper, we used a SNS stroller in Disney world for the kids (age 3 and 6.) I can't wait to use this with my girls:)
**Also, these pics are off the One Step Ahead site. Love the transracial family:)