Share your insights or perspective on the financial matter presented in the input.

Why might a robo-advisor service like Betterment be preferable to just buying a single well-performing index fund like SPY?
Diversification and convenience: Is .15-0.35% fee worth it? It depends on your net worth, amount you invest and value of your time (if you have high net worth and low cost of your time the fee is highier then in case when you have low net worth but high cost of time - so Betterment seems to be a better option to young professional just after college then to someone already retired), your interest in finance, your willpower etc. Is Betterment allocation better then pure SPY? From what I understand about finance theory - yes. EDIT (as requested) I don't have any affiliation with any financial institution as far as I know. I opened it to get used to just investing as oppose to saving and ups and downs of market (and read up on the portfolio management, especially index funds) and I guess it worked well for me. I plan to move out entirely out of it once the cost of the account would be more then paying for a few coffees and move the account to Vanguard, Schwab or something similar.  In other accounts (HSA/...) I use simpler portfolio then the Betterment one (US Total, Small Value, Developed, Emerging and Bonds) but there are people who use simpler (search for 3 fund portfolio).