Let me remind you that overclocking is for big boys or who are performance, serious users. We can amplify our computers by configuring hardware devices to perform better than default or making it beyond its capability. Overclocking may result in serious injury and there are a lot of risks involved in this process. So you have to take care while increasing the frequency of your GPU.
I think the damage is up to you, it is the estimation of how much you push your device’s clock speed. In my opinion, overclocking is nothing more than overheating, you can perform safe overclocking which will result into increase in performance. On another hand, if you will misuse afterburner your GPU will be definitely burned.
Read Also, The process of overclocking AMD GPU