The need for a shotgun microphone arises when you want to remotely capture a sound that originates from a short distance away. They provide a narrower angle of acceptance that isolates the subject's sound from unwanted "off-axis" ambient sound. Example: The noise from a computer that is running in the room where the interview is going on, the shotgun mic. will give you better isolation.
The way these microphones capture sound from a distance is similar to holding a paper towel tube up to your ear. The longer the tube, the more focused the sound will be.
A misconception about shotgun microphones is that they can pick-up sounds across long distances. If you're recording a person who is speaking, you wouldn't want your shotgun to be more than five or six feet away from them. The closer the subject is to the microphone, the better it will sound, which is why boom poles are commonly used.
When we are on a shoot we will get the shotgun mic as close as possible. Just check with your camera DP person to make sure the mic. is not in the frame.
On an outdoor shoot, the wind sock or blimp is a must for the shotgun mic. when wind is a issues. It often works better then a Lavaliere mic. with a wind screen.
