Finance is the Domain equivalent of rooting around in the couch cushions for loose change so you can pay the pizza delivery guy, or maybe taking that two-week part-time retail job during the holidays for some extra spending money. It doesn't directly have anything to do with the P&H or province income, nor is it limited to landed domains - it's your regent finding cash wherever he can. For a guilder, it might be cutting a few quick deals or disposing of surplus goods in a fire-sale; a landed regent might be selling off some minor holdings or shaking down some lesser nobles who've been behind on their taxes; a wizard might be making some 'love' potions or other minor charms and spell-casting for noble families willing to pay. It's usually stuff that's not really sustainable in the long-term, but it nets a small amount of GB in the RIGHT NOW. If you have an action you just don't need (who ARE you and how did you manage THAT?) or you're totally strapped for income, it's a reasonable move to make.... occasionally. Regular use, however, will accumulate more and more consequences as you squeeze every source of income dry.