What is NUA?
Net Unrealized Appreciation is the increase in value of company stock inside your 401(k). Normally everything you withdraw from a 401(k) is taxed as ordinary income. With the NUA strategy, you take the company stock out in-kind, pay ordinary income tax only on the original cost basis, and pay the lower long-term capital gains rate on the growth when you sell.
When NUA makes sense
NUA works best when: your company stock has grown significantly, your income tax rate is much higher than your capital gains rate, and you're doing a lump-sum distribution from the plan. If the stock hasn't appreciated much, a regular rollover to an IRA is usually better.