If you are invisible, you can't be seen with the naked eye, but you can do an awful lot of spying. When you do something embarrassing, you often wish you were invisible.
Germs are invisible, as are odors. A good question to ask someone is whether they would rather be able to fly or be invisible. Flight gives you freedom to travel, but if you are invisible, you have the ability to sneak around and see things you would not normally be able to see. Which would you prefer?