In the earlier days when I used -alt-preset standard with 3.90.3, I was told that -q 0 could potentially harm the quality of the MP3-file created. Now, when the VBR modes -V0 through V9 are equivalent to the -presets (3.96.1), I would imagine that using -q 0 would only potentially increase the quality. Is that so? If not, why not?

Nowadays -q 0 can safely be used with the VBR presets. But the increase in encoding time ist most likely not worth the increase in quality.