Tax-free growth at compounding interest, beating inflation, diversification to mitigate risk & lessen volatility (eg, not putting eggs all in 1 basket). Markets always have risk: if you're really afraid of risk, you can shift to mostly low-risk types of investments (bonds, money market, cash equivalents, etc). Real estate is typically considered riskier.
Retirement isn't necessary: qualified distributions (no tax penalty) only require reaching a certain age or any of the many exceptions (including terminal illness). Early distribution with tax penalty is always possible.
It's all basic information a certified financial planner or advisor or some articles on the internet can tell you.