Be warned, your brake light switch may be malfunctioning and it may cause an accident.
The brake light switch won't affect your brakes or stopping power, however the brake light switch is the only function that lets the rest of the car know that you are pressing your brakes. Your brake lights won't turn on and you will not be able to switch driving gear position.
Here is one way to check: When you are having trouble switching gears [ie. 'Park' to 'Drive' on an automatic transmission], have a friend check your brake lights. If the lights aren't turning on while you are holding the brakes, the brake light switch has malfunctioned.