It comes down to time frame. If you need the money in a short time frame, stocks/bonds are not going to have a high confidence interval in having the same or more value at the time you need it. So, say, saving for a car 3-5 years from now, probably better off putting it in high-yield savings.

But a retirement dream home 20 years from now, throw it in stocks and bonds according to an asset allocation[0] you're comfortable with.

[0] https://investor.vanguard.com/tools-calculators/investor-que...