There is a button on most rollover forms that says something like "roll entire balance to IRA."
For most people that button is correct and boring.
For a smaller group it is the single most expensive click of their financial life, and there is no undo. Once company stock lands inside an IRA, a tax provision worth potentially tens of thousands of dollars is gone permanently.
The provision is called net unrealized appreciation. NUA, if you want to sound like you work in benefits.
It applies to exactly one thing: shares of your employer's stock sitting inside your 401(k). Not stock in your brokerage account. Not stock options. Shares of the company you worked for, held inside the plan.
If that describes you, the next fifteen minutes are worth more per word than almost anything else you will read about retirement accounts.
If it does not, you can stop here with one sentence: check whether any of your 401(k) is in company stock before you roll it anywhere.
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Most people have never looked.