I'm not as familiar with what AMD does with their turbo, but I'm sure it's similar to Intel's. The idea is this: Base clocks are what you're guaranteed. A CPU (unless it throttles) will always give you at least base clocks. A CPU will spend time above its base clock, up to max turbo, until it's told to slow down because of TDP or temperature.
Generally desktop CPUs have high enough TDPs and enough cooling that they are always at max turbo. Laptop CPUs, and those in smaller mobile devices, may go up to max turbo for brief periods, for instance long enough to load a web page, but can't sustain it due to cooling requirements. By having turbo, you are able to briefly have performance above what the cooling in a device could otherwise support continuously.
