Aliston is referring to a specific circumstance that screwed many employees during the dot-com boom. If you
exercise your options, that creates a taxable event for the difference between your option strike price and the fair market value of the stock on date of exercise. If the stock price subsequently goes down a lot, you can end up with a tax bill greater than the market value of the stocks when the lock-up period ends. It was generally advantageous for employees in the rising stock environment of the dot-com bubble to exercise their options before the IPO, or shortly after. For one, it starts the long-term capital gains timer going, so you can sell for LTCG rates 6 months after the lockup ends rather than a year. Two, the difference between your option strike price and exercise price is taxed as income (usually - for NQs and ISOs over the AMT, but not ISOs in low tax brackets), but the difference between exercise price and sale price is taxed as capital gains. That created a situation where many employees had tax bills on stock worth less than the tax bill.
This situation doesn't apply when you have straight RSUs that you sell when the lockup ends. These are withheld at income tax rates when vesting, and then taxed as capital gains rate when you sell. The IPO price doesn't matter in this case.