If you google "Why cane rods?" you'll find many interesting answers. People ask me this question all the time. Usually, their point of reference is a graphite rod. Often, too, they have some misconceptions about cane rods. Here are some of the topics that almost always come up.
Weight. Solid cane rods can be heavier than hollow graphite rods, especially long cane rods. For the most part, there are length constraints on cane rods that are less generous than on graphite rods. It would be almost impossible for me to make a 10', 4 wt. cane rod suitable for Czech-style nymphing. Cane rods used for normal trout fishing -- wet-fly, dry-fly, streamer -- under 8 1/2' in length that are very close in weight to comparably sized graphite rods are achievable through hollowing and the choice of ferrules and hardware. "Close in weight" means that under normal fishing conditions, you would not notice the difference. As for Spey rods, the same results holds for rods under 12' or so.
Slow. Preferences for what is essentially "stiffness" in a fly rod have changed a lot over the past century. Many cane rods were made during a period when a "wet-fly" action was deliberately slow to keep from breaking the leader on a take, but there were also "dry-fly" rods available then that were just as "fast" or stiff as modern graphite rods. A cane rod can be tapered in many different ways to suit different fishing circumstances. Stiffness is all about taper, materials, and production process. Because of the capital intensity of producing graphite rods, there are more limitations on the ability to custom taper graphite production rods than on cane rods. Hollowing appropriately tapered cane rods can produce casting instruments with similarities to graphite in terms of stiffness, if that is desired. One of my measures of casting quality for a rod is whether it loads and casts a nice loop at normal fishing distances without hauling. Most of my rods have this characteristic. In my experience, almost all graphite rods require hauls for loading because of their stiffness. Loading a rod has complex dynamics that are usually addressed best through tapers.
Fragile. In my experience, cane rods are no less fragile than graphite rods and, perhaps, less fragile, because cane rods are not completely hollow cylinders; even hollow-built cane rods have solid dams that provide hoop strength. The same shocks that would break a graphite rod could break a cane rod, too, but perhaps not. Cane rods rarely delaminate, unless they're really old. See the "Cane Care" tab for more information on this topic.
Expensive. Cane rods are often expensive in terms of initial cost. My rods cost a little more than twice of what a premium graphite rod would cost. While almost all rods depreciate in value over time whether they're graphite or cane, there's more interest in cane as a collectible than in graphite. The secondary market for most cane rods is more active than for most graphite rods. While collectible or investment appeal is always a possibility for cane rods, the return on the premium paid for a good cane rod almost always comes from the enjoyment of using it and the pleasure of passing it to the next generation at the appropriate time. Good cane rods have an appeal over time that I have not witnessed (yet) for graphite. Moreover, they will last generations if cared for properly. If a problem occurs, there remains a group of cane craft enthusiasts that specialize in repairs and restorations.