One thing that I think is often overlooked is the maximum amount that can be contributed to a 401k. Often times, people say that it's 19k (for 2019). This isn't totally accurate. You can currently contribute 56k total into a 401K.
* 19k maximum in tax deferred contributions
* + employer match
* + after tax contributions, up to the max of 56k total dollars.
You can contribute even more than this if you're 50 yrs old or older, due to the "catch up" provision.
For those pursuing early retirement, the 72t clause (also called an S.E.P.P.) mentioned by
@BlackSheep is a good way to access your 401k before age 59-1/2, but make sure that you work with someone well versed in this because if not done properly, it'll trigger early withdrawal penalties. Also, once you flip the switch on a 72t, you can't turn it off until 59-1/2.
There's another option for early retirees, called a Roth conversion, where you can take money from your 401k and convert it to a Roth IRA. This is particularly good if you find yourself in a position where you don't have taxable income (yet) in early retirement, . A roth conversion is a taxable event (the IRS considers it as income), but if you have no taxable income for the year, and roll $24,400 (the 2019 standard deduction for married couples) then you won't pay any taxes on that money. (This would drop to $12,200 if youi're single) You have to wait 5 years to use that money, but this is one way to have completely tax free money in retirement. Some people repeat this process every year, staging the money for use in year 5, 6, 7, 8, etc. This technique is called a "roth conversion ladder" for those who want to look up more info.
TLDR...
Tax deferred contribution (to a 401K), rolled to a Roth (without paying taxes), for later withdrawal from the Roth (tax free).