It used to be philanthropic stuff - because buying public opinion/legacy is pretty expensive. So you fund a big charity, do some speeches, and are celebrated for being so generous. Has the side effect of actually helping some poors.
Seems like the major expenses now are donating money to fascists and buying big boats.
But $1B (at today's levels of value - the number isn't the issue, the relative value and lost opportunity cost of distributing some of this back to the people is the issue) is an obscene amount of money. You could invest it in some safe asset making 2% per year and yearn $54k per day ($20M/year)