Several days ago, a commenter on CNBC noted that garden-variety money market funds were offering higher SEC yields than garden-variety total stock funds (e.g., VTSAX). That twirled my head a bit, so I checked it out. He was right. The SEC yield on VTSAX is 1.83%. For VMMXX, it's 2.06%.
Granted, VMMXX has no potentiality for appreciation, but neither has it the potentiality for depreciation (unless Vanguard "breaks the buck").
That said, 23 bps does get one's attention.