What is best default value for JPEG image quality (as of popular ⟨libjpeg⟩ quality scale)?

So, it's (a) 75 for being that "the resulting reconstructed image is usually nearly indistinguishable from the source image"; (b) 50 is "based on psychovisual thresholding" and "have been used with good results".
So, why is that:

Почему мне пора слезать с ⟨Wolfram Mathematica⟩

(Одна из самых популярных программ для разных математических вычислений, в т.ч. символьных.)
Списком: