Wading is fast water is often a challenge. Unfortunately, many river booties made these days have very slippery soles on wet surfaces. Sometimes using a paddle as a cane isn't convenient. If you have a rescue vest with a tether and someone to belay you from upstream, that line will provide a great deal of support. It also provides significant safety since your belay person can quickly keep you from getting swept downstream should you slip and fall. Using two lines as in a traditional v-lower is even safer.