It looked like CloserToFine's spouse was going to increase donations. It's this extra I considered 'spare'.
On the other hand some people will always spend up to or beyond their earnings level, so whether they are paid well or poorly they never have spare cash at the end of the month.
I guess giving it all away to billionaires is never a good idea though:
(Proverbs 22:16) "The one giving gifts to the rich will end up in poverty."