One big reason is that he can time the actual donations, for tax purposes. That allows him to make big donations in years where he has large amounts of taxable gains to offset. If he donated $1B this year, he'd likely hit a deductibility cap (especially if he donated to a private foundation, as opposed to a generic 501(c)(3)).
https://www.nytimes.com/2015/12/03/technology/zuckerbergs-ph...
This is a dynamic system, so changing one parameter would cause other parameters to be changed as well.
Of course, a savvy parent would put pre-IPO stock into a trust, using up some portion of the $5-10 million exemption amount (it's up in the air because some of the Trump tax cuts are not permanent). Millions of dollars in pre-IPO valuation stock turns into tens or hundreds of millions by the time you die. And there are more nuanced (and/or aggressive) strategies that can yield greater results — or at least that's what I remember from my trust and estate law class.
Also, of he's giving the money to his LLC, is this deductible at all?
Edit: thanks y'all for your answers, I didn't think to check the rest of his Twitter timeline to see if he already answered that question.
Basically more control.
Emerson Collective (Laureen Jobs) is probably the most prominent example.
> Why is #startsmall a LLC? This segments and dedicates my shares to these causes, and provides flexibility. Grants will be made from Start Small Foundation or the LLC directly based on the beneficiary org. All transfers, sales, and grants will be made public in tracking sheet.
Private + non-profit combinations are not uncommon. I'm not sure about the specifics in the US, but getting the status as a non-profit acknowledged is also a PITA in some jurisdictions, especially if he dedicates part of it to non-traditional causes like UBI.
I find the division between those who are donating or pledging, vs those lining up for a handout, far more interesting.
https://www.sfgate.com/news/article/Behind-the-scenes-privat...