As it turns out, this particular YouTuber—Big Clive—is quite a good source of information. He has a very substantial practical experience and doesn’t claim to know everything. He happily corrects errors, which are uncommon even in his large body of work.

Clive is one of the Good Things™ about YouTube.

Big respect for Big Clive but I would never say no need to clean flux. On some of my old boards you can easily tell where I got lazy with the flux cleaning.

https://forum.allaboutcircuits.com/threads/memio-emulator-for-z80.117003/

 

Well, none of the things I make now will ever see an industrial environment.

Kitchens and bathrooms can come pretty close but just not continuously.

 

Big respect for Big Clive but I would never say no need to clean flux. On some of my old boards you can easily tell where I got lazy with the flux cleaning.
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https://forum.allaboutcircuits.com/threads/memio-emulator-for-z80.117003/

Well, he was reporting on empirical data. Who knows just what flux he used. The modern no-clean fluxes can be left on the board according to the manufacturer, and they are also water soluble. The volatiles previously used for flux cleaning became a nightmare for disposal.