Automatic fallback from \fussy to \sloppy

Question

1. If I activate \sloppy document-wide, will the paragraphs that render well with \fussy be affected?
2. If answer to the above is yes, is it possible to have \fussy by default, but automatically enforce \sloppy for paragraphs that give overfull \hbox warning with \fussy?

A fussy-sloppy example

Answer 1

As mentioned in the answer to the other question, this is basically achieved by not using \fussy which sets \tolerance so affects all paragraphs, but by just setting \emergencystretch which only affects paragraphs that would otherwise have had over full lines.