Why can you use electrolytic caps as coupling caps?

[Benta]

All valid and sensible points.
But 3 and 5 are not applicable to this discussion, so we've gone full loop here.

[Vovk_Z]

On the same book Self gives some clues about why such capacitors are much larger than initially thought. It is related to avoiding/minimizing distortion caused by the caps. See chapter 2.

I don't have the book. but minimizing distortion by using electrolytic output caps without DC bias seems way out.

It about minimizing distortion by using larger electrolytes. The larger is capacitance - the smaller is AC voltage across a capacitor and the smaller is distortion.

[TimFox]

All valid and sensible points.
But 3 and 5 are not applicable to this discussion, so we've gone full loop here.

Note 5 is directly relevant to operating an electrolytic capacitor without DC bias, which is part of the original question.
Note 3 is about what Mr Self actually said in his book:  reduce distortion by using a larger than required capacitance.
Self never said that removing the DC bias improves the distortion.

[vk6zgo]

I understand that one of the basic design ideas of Self is how to make things cheap and simple. That's why cheap polar electrolytes instead of non-polar or instead of a film types. They work fine too if you just want to make things done and if you are fine with 0.00x % distortion instead of 0.000x %.

If we factor in the imperfections of human ears, The difference is negligible.

As to electros---there are millions of audio stages that use the polarised type with no ill effects.
I don't like them personally, from my perception of their possibly poor reliability but they seem to have "hung in there" for so long that there seems little reason to avoid them.

Non-polarised electrolytics can have quite poor ESR in my experience & are often large enough to be hard to use for replacement during repair.
It is only relatively recently that film capacitors of equivalent values have been small enough to replace low value electrolytics.

During the mid to late 1990s, the monolithic caps I used in values up to around 1uF or so were small enough to replace the myriads of electros around such values that Sony used in their equipment,
Any capacitance values much above that became prohibitively large.

Cathode bypass capacitors of around 25uF were extensively used in tube amplifiers, & were effectively in the signal path, as if they failed to a high impedance state, the cathode bias resistor would cause a loss of stage gain due to negative feedback.
If they "gracefully" failed, reducing their effective capacitance over time, the stage frequency response would deteriorate.