I laid over once at South Canyon. It was a nice break after the hectic travel to put in, rigging, etc.
The downside was that it backed us up into the trip launching the day after us and for quite awhile thereafter down river we were stacked up, competing for camps and leap frogging down the river.
Seems like if you stay in the standard mileage plan that most people follow (10-15 miles per day) for the first several days, you don't see anybody for the first week, which is nice. Unless, of course, you get some eager beavers launching after you and then maybe South is a good layover so that they get way ahead of you.