I use the cortland 160g nymph line. It also comes in 140 and 120. You don't pick the line on rod weight, but instead on the weight of the flies. 160 is for heavy nymphs (I use in large water ways with fast current), 140 is for medium weighted nymphs, and 120 is for lightly weighted nymphs (think spring creeks). It is important to match these lines with nymphs of the appropriate size, if you want to maintain a good drift and contact at distance.
A 160g line will pull lightly weighted nymphs back towards you, if the nymphs and not properly weighted. For example on Penns, I use the 160g line with tungsten beaded woven flies/stoneflies/whatever heavy fly you like, and using a 10ft leader, I am able to get about 10-15 ft of fly line out of my rod and maintain constant contact and good drift. This is while using a 10ft rod. So add this up and you can tight line in any direction about 30-35 feet from where I stand.
Using the same set up with a size 16 nymph, the fly line is too heavy and pulls the fly towards me and out of a natural drift. So if I were going to buy one for say Spring Creek, I would use the 120g.
I usually use the nymphing line, when I know I won't be looking for dry action. But I bring an extra spool with a normal line, so I can actually cast properly.
The rio 'nymph tip' is not the same as their Euro nymphing line. The nymph tip was made for flopping big strike indicators over with tandem rigs. A nice line for that, but not so nice for tight lining. (Comparatively)
I bought a line because I wanted to try it and had the money and plenty of extra lines for my rods. Would I buy a 'nymph line' if I only had one spool for my reel and no other lines for a rod, NO.
You will enjoy them if you get one but they are expensive and like others said, you can get along perfectly fine without spending money on one.