Now that I’ve been on several official boards of advisors for a few years I can report:  boards of advisors are almost never asked to give advice, though they do sometimes offer it anyway.  But boards of advisors are usually "boarded", i.e., paid something.

They would be better called "boards of prestige" – the message being "we aren’t so clueless that these prestigious people refuse to associate with us."  Or perhaps just "we could afford to buy these prestigious people, even though for a price they’d associate with anything."  Now I have in fact turned down paid affiliations with organizations I thought too clueless, but I can’t report how many others are willing to do the same.