Do you feel unsure if you are investing your 401(k) optimally or wonder if you are earning too little return on your money? These are all questions that a good investment plan will cover.
You can play with the allocations of different assets to understand how your savings may grow with more savings in risky assets (such as stocks) as compared to bonds or cash.
I always recommend diversifying using index mutual funds or ETFs. These funds allow your investment to gain all the benefits of growth and dividends while removing most company-specific stock risks.
You should test several different allocations between stock, bonds, and cash (and for more sophisticated investors- commodities, real estate, and alternative types of investments) to determine what total value your net worth could grow under different allocation options.