Context: I have given around $1000 to GiveWell this year and I am considering giving around $1000 more. I'm a college student, so that works out to around 10% or 20% of last year's income.
It seems like EA-aligned causes and professional grant makers like the FTX future fund have more money than they know what to do with; the general consensus on the forum appears to be that EA is (for the moment, at least) no longer funding constrained. If this is true, the case for direct work seems very strong, but the case for personally giving seems weak.
I don't expect to do better than e.g. William MacAskill when selecting funding opportunities, and if he thinks that last-dollar funding is not cost effective, why should I? (I know that professional grant makers think that last-dollar funding is not cost effective because they aren't funding more projects, but aren't out of dollars.)
In other words, professionals I expect to be able to make better decisions then I am think that marginal EA-aligned funds are better saved than spent right now. Why not do the same for my personal giving? If the EA landscape doesn't return to being funding constrained, why ever give more?
With respect to the last dollar of funding: I think Open Philanthropy expects to spend their last dollar on something more cost-effective than GiveDirectly. So I think the last dollar of spending will still look good, and at the worst case your spending now will move some other funding to something somewhat less effective but still pretty good down the line.
Another potential advantage for an individual donor would be identifying something not currently receiving large amounts of funding that you think is worth taking a bet on. That would give the initiative more time to demonstrate it's value and to gather information on how well it's achieving its goals (or it could be funding an individual to grow their skills or something).
We've also seen Will write that the FTX Future Fund rejected 95% of their applicants, so it's not the case that there's a money firehose that everyone has access to. Plenty of people are, presumably, open to working on new projects given funding.
None of our big donors were intending to spend all of their funding before now. It's taken Open Phil years to grow their capacity and increase their giving in line with their standards of diligence. They intend to spend down their funds, I believe, within the lifetime of their funders.