Money Market vs. Cash? What’s the difference? Also, what are current cash (and equiv) yields on Fidelity, Vanguard, Etrade, etc?

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SPAXX 7 day yield is 3.33% Fidelity® Government Money Market Fund

FCASH yield 1.57%

https://www.fidelity.com/mutual-funds/fidelity-funds/money-market-funds-fcash

What is the reason to hold FCASH vs. SPAXX?

SWVXX is 3.76% (TDAmeritrade/Schwab)

VMFXX is 3.68% (Vanguard) VANGUARD FEDERAL MONEY MARKET FUND

Where do you park your cash ? Please post tickers