Explanation for why partial function are bad is missing

[soupi]

Discussed in #56

^{Originally posted by refaelsh September 22, 2022}
Here: https://lhbg-book.link/04-markup/02-parsing_01.html#partial-functions, in the second paragraph, it is not explained why it is bad. IMHO, an explanation needs to be added. I don't know what it is --> can't open a PR :-)