db had a comment that bears repeating and rings true in many cases.
He mentioned that triple portaging leaves you less fatigued at the end of hard portage portage than 1x--2x would in some cases.
My personal experience has been that its something to consider for all or even just the hardest parts of a long slog.
Unless your a ultralight road runner person who single portages every time, you won't find much difference time wise between 2x--1x portaging especially if while single your stopping or arrive so whipped you need time to recover.
Same with 3x vs 2x. Yes, your covering more ground, but expending probably little more energy running empty vs lugging a load.
I've often 3x portaged just short sections ( mud bogs/ corduroy) and found that the time wasn't that big of deal and when you factor in the fatigue/safety factor, it was really a no-brainier.