Certainly better than the cheaper stuff and all the "experts" use it but tons and tons of people do just fine without it. It's a cost/benefit analysis. Is the (relatively small) increase in performance worth the (relatively large) increase in cost? It's your money so only you can decide. For Euro-nymphing, the more important thing is just having a small diameter, level leader to allow the heavy flies to pull it through the water column evenly. One other thing to consider with fluorocarbon is that it lasts way longer on the spool so if you're the kind of guy who uses one spool for 2-3 years without running out, it might actually be cheaper to buy the fluoro once than to throw away and replace brittle nylon.