Another good use of DP's are smoke jobs, were i find they make meeting the requirements of 406.4 easy....
Let's say you've been called to smoke out an older apartment, all BX /KT wiring with ungrounded receptacle outlets
Now one could argue the 6' rule of 210.12(B) , coming off it , not disturb the original receptacle outlet (hard to do) and maybe use all plastic boxes where there is nothing to ground, yet you've still run an egc....
Since most antiquated wiring is a one circuit does all deal, one DP may well gain compliance , with particular note of 406.4(D)3 EX (also a new '14 inclusion) advocating their installs....
~RJ~