Dwight - Because leaders are tapered, everytime you cut off a fly and tie on another, it gets shorter AND the end where the fly is tied gets thicker. Tippet is thin, non-tapered line that you tie onto the end of a used leader to add length back and to reduce the diameter of the line at the fly again. You might add 18 or 24" of tippet and after a while when that gets short, cut it off and replace with new tippet.
The smaller the fly you are using, the thinner you want the line to be at the fly end so the fish don't notice it. I might buy 6 or 7 foot 6X leaders and they are great for small flies for BG. When they shorten up some, I either add 6X tippet (and continue using for small flies) or use them for throwing bigger flies for LMB.
Managing the line is all about fooling the fish. Fly line is big and obvious and will spook fish. A tapered leader is less noticeable to the fish and gets the fly away from the spooky flyline. When the leader gets shorter and the end gets fatter, it becomes more noticeable, so you tie on tippet.
Cisco - I don't see an advantage to 4 piece rods unless you're stuffing them into a backpack to access remote water. I've got one 4 piece, but now that I'm a bit older and less ambitious, it just sits in the closet.
