I happen to have the car cover from Honda for the 2010 Insight. No, you don't need to take off the antenna, before you cover the car. There is something to cover that also.
It's great for covering the car before it snows or if you're not planning to use the car for a while. The material is lightweight, breathable and dries fast after it gets wet from the rain or snow. It also looks nice too.
Id remove it, but the cover may have a hole or tube for it. I won a complete car cover for my scion xa. It had a license plate window, big scion logo on it and the option to make an antenna hole. I was told by many that its great if the car is parked in a garage with no or little wind, like a parking garage. THe bad side was that it gives cover to anyone who may want to break in and steal stuff. You cat see the window is broken or the security blinking light. Second, wind blowing can cause rubbing and scratches on the paint. Lastly, the cover too needs to be cleaned or washed just like the car.
Ive been tempted to buy a generic one from advance auto or big lots for a prius, but this paint just scratches too easily.