A wide angle binocular can be useful for beginners or children since it's much easier to find an object when you can view more of its surroundings. The larger the exit pupil the brighter the image. A large exit pupil is an advantage in low light conditions. There is a limit to this however. There are many other calculations that can be used to express differences between models such as relative brightness and twilight factor.
Relative brightness is the square of the exit pupil.
This is an attempt to quantify brightness. The twilight factor is calculated by multiplying the magnification by the diameter of the objective lens and taking the square root of the result. This calculation shows how resolution in low light can be improved with higher magnification. The simplest and most meaningful measure of brightness is the exit pupil. Other Considerations For birding and wildlife viewing close focus can be very important.