Waveform Function Generator - Practical Usage
You are right to say that they are very useful in audio applications.  But function generators are also very useful for filter design, Analog-to-digital converters, switched-mode power supplies, and many more. 

Here is one very useful example for a power supply unit.  Half-bridge, full bridge rectifiers produce a DC output essentially from an AC signal.  To raise the AC signal above 0V, you would indeed use a clamping circuit.  



Another example I can think of right now would be Analog-to-Digital Converters (ADC).  You could have a 10 bits ADC just like what the Arduino Uno's are.  Some the analog voltage would be assigned to a bit.  For example, 1024 would be 15V and 0 would be 0V.  512 would be 7.5V.  



A third example is filters.  Low-pass, high-pass, band-pass, and band-stop filters are some you could design and use an AC waveform from the function generator to test it.  

Finally, function generators are usually capable of generating a clock signal (square waveform) which can be useful for digital electronics and memory circuits like Flip Flop, Shift registers, and many more.  Here is what a function generator can typically generate: