One thing we haven't touched on - because this is about lines - are rods. We have assumed that the rod manufacturers get their line weightings right. And that there actually is a "right". This is by no means a given; determining rod weighting is far more of a subjective affair than you would imagine (see the Understanding Carbon Trout Rods thread).
Personally I think it's important to know where the line designer's 30' point is on my line.
Remember, that 30' point is the amount of line outside your rod tip that the manufacturer reckons hits the standard for your rod. Any line outside your rod tip before or after that point is less or more weight. I measure the line and mark the 30' point with a sharpie. I put another mark 10' further up (so at 40') so that I can see it when it arrives in my hand.
If you have a 9' rod, a 12' leader, 30' of line outside the tip plus another 10' or so to shoot (hence the 40’ mark) you're casting 61' from your feet. That's almost always more than enough and creates a pattern I find I need to keep my casting easy and consistent.
Of course rods don't stop working either side of that 30’, they're designed to work through a range of distances so there's no need to be obsessive about that 30’. It's just a useful visual guide.
