Thanks so much! I just sold my RSUs thanks to this info. Very much appreciated.
This is country specific. The stock grant price and the vest or sale price are used in my country to assess gains, so you still have capital gains to pay even if you sell right after vesting
Capital gains only covers the value increase over the year you hold the stock after its vested.
If you work at META, and then immediately on vesting diversify and don't touch the stock for a year you'll reap the same capital gains benefits but with a diversified portfolio.
You also have a wide range of defensive strategies you can apply that you can't if you're locked into trading windows. Say a META employee was very bullish on FAANG in general and at vesting put all their money in GOOG. If they were nervous about this week's earnings they could have either closed their position to see what happens, or bought defensive puts to lock in a maximum loss. Had they instead chosen to hold META they would have neither of these options.
There are cases for recently IPO'd companies where you vest then have a potentially 6+ month lockout period for trading. In those cases it can make sense , provided you have seen substantial gains in that lockout period to keep holding for tax reasons.