The second video says It all. If you change gain, sum or subtract you get around 3 dB to 6 dB noise depending on the correlation between the rounding noise.
But no one will ever hear if you add 6 dB noise at –138 dB on a heavily distorted guitar (although the guitarist will claim that it sounds better).
The funny part is that he properly would get the same figures if he had don the experiment in 64 bit floating-point. There will still be rounding noise even in 64 bit, although I admit that it will be added at around -306 dB.
I will rather have speed than bits. 