Everyone needs sliders on their streetbike. With sliders, you can fully drop your bike at low speed and pick it out without any damage. At higher speeds they will obviously bend or grind down completely and then some damage will naturally occur. BUT they will almost always save your engine and frame in the worst case crashes.
Here is an obvious case in which they definitely helped out but the severity of the crash was just too much for them to handle. There is no doubt that they did help though. Sliders are cheap insurance for sure. This bike was obviously racing in the water at a very high speed for this kinda damage to happen. Interesting pictures none the less.