Two fletch works great on lighter shafts such as POC, Sitka, and Doug Fir that are on the lighter side....this is because of arrow speed. Do a two fletch on Ash, Maple, Mahogany, etc. and you can easily see the instability in flight from 15+ yards.
I love two fletch/ as it's simply a matter of setting up your fletching jig to do the first fletch at 1:00, then when the glue is dry, just pull the arrow out, rotate it and fletch #2 at 7:00. Ezy Peezy.
There is only one other draw back to two fletch, while fletching this way allows arrows to nest together in quivers, it can actually put them too close together in a back quiver to easily grab by the nock if you shoot with a glove. Not a problem for tab shooters, though.