This was great timing for IBM employees with RSU's. Many folks had RSUs which literally unlocked this morning.
In fact, the ideal scenario is that the price drops just before your vest and then bounces back up after.
Assume an employee's marginal tax rate is 40% and their capital gains rate is 15%. Then there are 2 scenarios:
1. Vest 100 shares at $100 apiece. After tax that's 60 shares * $100 = $6000 total.
2. A sudden price drop causes 100 shares to vest at $50. After tax that's 60 shares * $50 = $3000. Later the price rises to $100 and the employee sells them. Another $3000 in capital gains, leaving $2550 after taxes. Total = $5250.
This is only true if you "sell" 40 shares immediately at the time of vesting to pay the tax bill. Because you lose the 40 shares, you don't have as much shares to appreciate in the subsequent upswing. However if you prefer to settle your tax obligations in cash instead, you don't have this issue and you'd actually pay less taxes (assuming the upswing does materialize). It's risky though, because you're basically taking a long position on the stock, and if it falls even more, you'd lose even more money.
I wasn't aware there's a choice. That's a paycheck withholding essentially.