My argument on this topic has always been that pretty much every large, unexpected personal expense that might arise can either:
A. Be paid with a credit card or
B. Can wait the 3 days or so it takes to make a stock sale and wire transfer or
C. As a last resort, can be covered with a credit card cash advance or a payday loan. These will cost you, but I think this scenario will almost never happen, since just about everything will fall under A or B.
The only thing I can think of are movie-style scenarios like 'your daughter has been kidnapped and held for ransom' or 'the mob is going to break your legs if you don't pay your gambling debts.' In the normal world, I don't think situations where you get a sudden expense for > $1000 and are expected to pay it the same day really occur, because
half of Americans say they could not cover an unexpected $400 expense. It is just not a practical expectation for creditors to have.
If there are some real-world scenarios I am not thinking of, I'd love to hear them.
I understand that there is a warm and fuzzy feeling that people get from having high liquidity, and if that's what you want, that's fine, but realize that the effects of cash drag are real. Good savings accounts pay about 1% (pre-inflation) these days. Vanguard founder Jack Bogle is predicting
6% annualized growth for US stocks over the next decade. If that is true, it would put cash drag at roughly 5%, or in other words, every $10K of liquidity is costing you $500 / yr. Not exactly small potatoes, and that is assuming below historical average stock returns.
Another way to think about it is that the cash drag on $10K is the same as the total expense on $1M invested in Vanguard TSM Admiral shares / ETF. So anyone who has found religion on using passive funds to minimize investment fees might want to take a look at how much money you are keeping in cash - there's a good chance it is costing you more than all of your investments.