General Bike Storage
Keeping your bike stored in a dry and safe environment, like a garage or basement is always the best option, but that isn't always possible. It is perfectly fine to store your bicycle outside, but keep in mind that maintaining your bike is a must. By going through a few simple procedures each month you will be able to prevent some wear and tear on your bike, whether you are storing it indoors or outdoors.
Garage Bike Storage
Storing your bike indoors somewhere like a garage, is often the best way of maintaining the bicycle. With your bike inside there is less chance that the apparatus will incur weather damage or other drawbacks like rust. Storing your bike safely away ensures that it will be in great working condition next time you take it out for a ride.
Outdoor Bike Storage
Keeping your bike outside isn't necessarily the best option, but sometimes there is no choice. As long as you keep your bike maintained, then keeping it outside shouldn't affect it's performance or abilities.