A major concern of the employees is what are the benefits of 401 k plans? The main advantage to the Primary 401k advantages to grow it tax-free, and the employer contribution option. These are 401k benefits that assist employees in steadily saving for retirement. Knowing what a 401k is helps you to better appreciate how little contributions can add up over time. The advantages of investing in a 401k over time are financial security, compounding and higher retirement preparedness.