You would begin to qualify for long term capital gains which is taxed lower than the higher end of your income, presumably. You can sell your stock 6 months after it goes public so if by then you qualify for a long term capital gain (1 year holding an asset) you get taxed at this advantaged rate. If you will likely make a substantial amount of money (100k+) this could be a lot of money you save.

Of course you assume the risk of being an investor and you could lose money if it all goes south!