3 Pitfalls of Only Using a 401(k) for Retirement - The Motley Fool

But while you definitely want to put at least enough into your 401(k) to earn the maximum employer match, using a 401(k) as your only retirement account may not be the best move.

If you're willing to branch out and put in the time to find the right investments, it's definitely worth putting some of your retirement money in accounts that give you more freedom. .

Distributions from a Roth IRA or Roth 401(k) are not taxed.

If you have access only to a traditional 401(k) at work and use it as your sole retirement savings account, you'll owe more in taxes in your later years than you would've if you'd put some of your money into a Roth IRA and taken tax-free distributions to help support you. 

Your 401(k) distributions are included when determining if Social Security benefits will be taxed, but distributions from Roth accounts aren't

If you put all your retirement savings into a 401(k) and withdraw enough to cross the threshold at which you owe tax on Social Security, you'll owe even more money to the IRS that you wouldn't have if you'd received some Roth income instead. 

Since you could reduce the size of your nest egg by getting hit with fees and limiting your investment options and get to keep less of your money due to higher tax bills, sticking with a 401(k) alone could really hurt your prospects for financial security in retirement