1. The much talked about question; or The much-talked-about question. If hyphenation is not required, would hyphenation make it wrong, and vice-versa.
Though I’d definitely hyphenate the following: “The much-talked-about-but-never-dealt-with question”. No?
2. I like groceries shopping; or I like groceries-shopping. Same for things like coat(-)checking, floor(-)scrubbing, etc.
How about: The groceries-shopping tedium; coat-checking etiquette; etc. Would it be okay if you don’t hyphenate them?
3. Behaviour is context dependent; or Behaviour is context-dependent. The page is content heavy; or The page is content-heavy.
Likewise, if hyphenation is required, would the lack of hyphenation make it wrong, and vice-versa.
4. The end of school vacation; or The end-of-school vacation. A not so surprising accident; or A not-so-surprising accident.
Again, the same question applies. Especially for the first case, since not hyphenating it would possibly change its meaning: The end of *the* school vacation vs. The vacation that happens at the end of school. Thus, can anyone, without hyphenating it, argue that they mean the latter?