Why Fish Double-Taper Fly Lines?

Remember double-taper (DT) fly lines?
If you’re new to fly fishing, it’s possible that you might never have seen one, much less explored its advantages. In fact they’ve been around since long before high-tech extrusion machines made fancy taper design possible. Author and historian Paul Schullery told us last night that double-taper lines were first marketed in the 1870s and -80s. But weight-forward tapers gradually became the more popular choice after they appeared on the scene in the 1960s. (George Griffith, founder of TU, claimed to have suggested the idea to Leon Martuch, founder of Scientific Anglers.)
To bring us up to date, Phil Monahan polled several experts about whether they fish DT fly lines and why. His article has already produced lots of interesting comments.