[rcxdude]

Not just eventually: many effects, such as basically any non-linear mapping like a distortion, will create overtones that will immediately alias down if you are not oversampling. You either need to use some DSP tricks or oversample (usually a mix of both) to avoid this happening, which often happens in just one step of an effects chain.

[scns]

A great explanation by Dan Worrall:

https://www.youtube.com/watch?v=-jCwIsT0X8M

[markkitti]

Even the term "oversampling" implies that sampling beyond Nyquist rate is excessive. I think you would agree that one is not being excessive. It is necessary to sample well beyond accepted "Nyquist rate" in order to reconstruct the signal.

[KeplerBoy]

I'd phrase it differently.

Your signal contains all kinds of frequencies: Those you care about and those you don't want in your recording. You can't just sample at the Nyquist rate of the interesting frequency and expect all the other frequencies to vanish. They will mess with the frequencies you are actually interested in.

[rcxdude]

That is the term, however. You see it in many contexts where a higher sample rate is traded for some other desirable attribute. (For example, it's often desirable for an ADC to sample faster than the higher frequency content you care about in an analog signal, for the reasons detailed in the paper as well as because it can give you a lower noise ADC. delta-sigma converters being an extreme case of this, helped by a seperate trick of noise shaping).

It's worth noting it's a tradeoff, even in pure processing: almost all non-linear transfer functions will create an infinite number of overtones, so it's impossible to avoid aliasing completely: you can only reduce them to some threshold which is acceptable to the application.