Re: Fluorocarbon tippet - different than fluorocarbn line?
BigJim's approach is a sensible one.
I cannot tell you what is best for you. You must decide that.
The key problem with any approach in fly fishing and this is especially true in nymphing is that we often do not know for certain why a fish refuses the fly. When fishing a dry fly we can sometimes guess at the possible reasons because we SEE the refusal, BUT when nymphing we do not even know a fish refused the fly at the last instant. The refusal occurs underwater.
So we may be getting a lot of lookers but no takers. What can we do to improve our odds when we can't even determine the causes of a refusal?
My approach has been to eliminate or reduce the possible reasons for a refusal. That is why I use fluorocarbon tippet material rather than line.
Can a few thousandths of an inch or even one-thousandth of an inch in diameter make a difference in drift, sink rate, and visibility? Even if it does, does it make a difference to the fish? The answer to your original question is that yes there is a functional (diameter vs strength vs suppleness) difference between regular fishing line and tippet material. The next step is that you must decide for yourself whether the type of fishing you do needs tippet or line material.
For the locations I fish, my decision has been to use the strongest, thinnest, and most supple tippet I can find.
"Discovery consists of seeing what everybody has seen and thinking what nobody has thought"..........Szent-Gyorgy