Furled leaders shine in delicate presentation of smaller flies. The whole energy management/dissipation curve is nicer.
For laying a big old fat bug out there with a plop, they are not at all necessary. But they sure do cast nice!
I got out of the furled leader business a while back. Just wasn't viable for me. But there are plenty of folks out there who do sell them and, truth be told, it's not a huge investment to set up and learn how.
"have fun with this stuff"
in memory of Big Dale
RRhyne56, Flyfishing warden