Edit, Matt I believe what you are referring to is more relevant for a rifle scope with a single objective.
Nope, applies to binocs too. The optimum size would be 7×50, they have the largest exit pupil, meaning best low-light performance.
However, a 50mm objective lens is a lot of glass, and as a result, heavy binocs. Also, the higher the mag, the narrower the field of view, so slight movements of your hands makes for greater movement of the viewed object.
It’s all compromise, get the best you can afford, in a size that you can comfortably carry all day, with the brightest image.