You employ this rigging when you want to rappel on a single strand while another person rigs on the other strand. See photo. This solves a typical problem with 2 strand contingencies of not enough friction on the unweighted side. When a lower is required, feed up all of the unweighted side, unravel the munter/remove the unweight strand from the figure 8. Put your brake hand between the stone knot and the munter/figure 8 biner and pull the toggle. I think (not tested) there is such minimal weight transferred to the fiddlestick that you could probably substitute a regular carabiner stone knot and still be able to remove it later.