The lines? Because if you set it for 40 psi, and only dispense with 6 foot lines, it'll blast out and foam like crazy. You need longer lines for higher dispensing pressures. For rootbeer, I use about 25' of line.
I bought some cheaper line from Mcmaster-Carr. I think it was about $.15/foot. It's more rigid than regular beerline, but it's food safe and works great for soda. I assume it'd be great for seltzer, too, then. There isn't any taste at all in that line.
I think it was kal who first posted that info on the tubing from Mcmaster-Carr. I know that beerline at the homebrew store is outrageously expensive, when you're buying 30 feet of it! This other stuff is smaller OD, and it "rolls" up really well, so that you can just put a twisty tie on the excess and it's not taking up too much room. I'll see if I can find the link.