The SQL file in the dump contains all the private messages sent on the site. It's likely that many Patreon users will be embarrassed by the nature of those messages, e.g. they are getting paid by unsavoury individuals, being encouraged to harass and abuse other people for money, or speaking candidly about their motivations (e.g. bigotry) while trying to maintain a respectable public face.
There is also information on who is funding whom, so a lot of people who might have wished to remain anonymous will now be exposed as e.g. supporting GamerGate or anti-rights speakers. As well as social repercussions they might lose their jobs etc. Remember how people reacted to Eich's support of an anti-gay-rights bill.