Ok so let's say you're married, couple kids, lower 30's. Mortgage is your only debt. Have extra money at the end of the month sitting in your checking. Do you contribute more to your 401k? Invest somewhere else I don't know about?
How much extra money? If it is just a couple hundred bucks and you have good choices in your 401k, invest there. Otherwise, depending on your income, start a Roth IRA.
A couple hundred bucks per month (give or take) could get you nearly halfway to maxing a Roth. If you are maxing your employer match on the 401k, wouldn't it be better to just put what you can in the Roth?
Short answer: Yes, but probably not too significant. I love the idea of a Roth, but I have that in my 401k as well.
However, sometimes people are intimidated by starting something new. Adding $200 per month to your 401k contributions is actionable in about 2 minutes. Setting up a Roth IRA seems more daunting to some.
What I invest in on a monthly basis:
Roth 401k (this is the most significant)
Roth IRA (not actually monthly, but a couple of times/year I make a contribution)
Company stock (buy at 15% discount. Have to hold for a year, but I now sell some 3-4 times a year. I don't want too much money invested in company stock)
3 529 savings accounts
HSA