Of course the better sports drinks have benefits over plain water. They can replace electrolytes, provide additional energy AND rehydrate. However, you may experience some gastric problems with the wrong drink or too much of any drink. For most it is usually better to drink both. Only time and experience will tell you which one is best for you and how much of it you can handle.
Last summer, it took me a few months as a new rider to work out what works best for me. 2 bottles of half-strength Gatorade, a banana and half a power bar keep me going on a 50 mile ride, (my longest ride thus far). As the above posters have said, you need to experiment with what works best for your stomach. Some people can eat/drink anything with no problems. I know guys who stop in the middle of a century and have a pizza and a few beers! That would probably kill me. When I first started, I had all kinds of stomach problems, but now it's pretty much under control. Good luck.
It depends what sort of riding you are doing as to whether you need this stuff. If its just recreational or slow training, say two hours max, you don’t need it. Plain water and a banana is fine and in fact is better for you. For racing or longer rides at higher intensity say 4 hours, it is of value but you need to eat as well, bananas, honey sandwiches and boiled spuds are good. For racing I like a bottle of plain water as well as one mixed with powerade. The stuff can stick your mouth together when you are going hard so plain water is better at certain stages. Some of the preparations don’t have enough of what you are likely to need anyway so you might want to look into it. I’ve found that powerade has both sufficient salt and carbohydrate to be of use for cycling. Others like staminade have plenty of salt but less carbohydrate and gatorade is under the minimum recommended level of carbohydrate and so is of limited benefit as well.