A lot of good responses. Longterm, cash seems a problem in these days of .001% interest.
However,
1) as several have noted, cash is its own entity, as an asset class. I hold 15%, although my allocation calls for 10%
2) in a world where corporate bonds are yielding less than 3%, 0% for cash is bad, but comparatively, not that bad
3) personally, I reaped cash in 2014-2015 as the market continued to run up and anticipating early retirement, also putting the DW's bonuses largely into taxable accounts, largely in cash. We had two houses, one in Houston and a Colorado cabin and I couldn't predict when or if they would sell or for how much. Also when or whether DW would find a job in the new location out West.
Cash in a taxable account gives enormous flexibility for the change to early retirement. It certainly reduced the level of our headaches in buying a 3rd house while we were selling two (20% down and then using equity to reamortize, along with moving expenses, etc.)
4) After settling, you can redeploy cash in a taxable account as an investment, which is pretty much what we will do, to take advantage of tax loss investing and as yield. I will probably build cash in 401k/403b account as this shift takes place.
5) "Excess" cash in tax advantaged accounts can be deployed to take advantage of market slumps--if you have the courage to do so, which isn't common. I did some of that in early February--and then the market went up rapidly. (I had assumed a somewhat longer slump, and I was wrong.)