Should I keep money in a high-yield savings account or invest it instead?

It depends on the time horizon, not the interest rate. Money you'll need within roughly the next 1–3 years – your emergency fund, a down payment, a planned big purchase – belongs in a high-yield savings account or similar safe place, because the stock market can drop right when you need the cash. Money for goals 5, 10, or 30 years out generally belongs invested, because over long periods stocks have substantially outpaced savings rates and protected you against inflation. A tempting high savings yield can lull you into parking long-term money in cash, but cash quietly loses purchasing power to inflation over time. The practical split: fully fund your emergency reserve and any near-term goals in savings, then route everything beyond that into a diversified, low-cost investment portfolio. See the trade-off in dollars at wealthserene.com/tools/opportunity-cost.