Is there any downside to keeping all my options or stock shares for as long as possible, hoping to score more profit if the share price keeps going up?

Yes, holding too many options or shares (as a percentage of your total wealth) can expose you to concentration risk. Having too much of your money is a single stock increases the risk that, if the stock price goes down, you might lose a significant portion of your worth. If you have enough assets or earning capacity elsewhere, you may decide to tolerate a higher degree of concentration risk with your equity compensation, hoping to “strike it rich.” On the other hand, if your financial well-being depends on keeping profits already achieved, it may be time to reduce your stock and stock option concentration risks. A general rule of thumb is to avoid having your company stock + options exceed 10–15% of your total wealth.