Whatever you can do with cash, you can also do with Bitcoin. Buy groceries. Invest in companies. Donate to charity.
But Bitcoin is capable of a whole lot more. Besides the ability to instantly send money all over the world, Bitcoin can enable you to do other things like:
Prove ownership of funds without ever having to show anyone else the funds (or your Bitcoin private key).
Anonymously run websites and publish content online. *
Anonymously buy illegal items on the internet. *
Gamble your wealth even if gambling is illegal in your country or jurisdiction. *
Safely carry vast sums of wealth across national borders without having to declare anything of value at customs.
Hide your wealth from a spouse during a divorce.
Protect your wealth from being seized by law enforcement.
* Keep in mind that remaining anonymous with Bitcoin requires additional action. Additionally, some of the above activities may still be illegal in your jurisdiction even if you use Bitcoin to do them.
For a near complete list of everything you can do with Bitcoin, check out the links below.