Really? For what purpose?
On the upside, any case where one is engaging in high-value transactions (broadly speaking). Knowing a negotiating counterpart's likes, dislikes, communication style, et cetera can help one avoid mistakes, build a personal connection and draft (and frame) terms correctly on the first try.
More seedily, such information about a political opponent (whether a politician, rival on a commercial or non-profit board, or commercial competitor) is useful.
As a risk mitigation tool, such data would find a natural home in a due diligence file. Prospective executives, board members, business partners, political donation recipients, et cetera expose one to reputational risks. Catching those in advance is already worth tens of thousands of dollars of legal time.
I would hate to live in a country where the above is legal. We should recognize the value of the information every single single Facebook employee has routine access to.
Well, apart from post-factum incarceration.
I recently downloaded my Facebook archive [1]. If it were legal, I would certainly pay thousands if not tens of thousands of dollars for certain peoples' archives. I can think of several practical contexts in which an unethical actor would find it profitable to pay a Facebook employee a million dollars for someone's Facebook archives.
[1] https://www.facebook.com/help/131112897028467/