Maybe I'm a newb. How does this bracket help you take pictures? It seems like a tripod head can hold the camera sideways just fine.
Most tripod heads do allow for a vertical position, but this usually moves the camera way off its position over the center of the tripod, and lowers it as much as 6 inches. So the camera camera & tripod combination is no longer as stable as it could be, or as steady, or at the height of the photographer's eye. And, composition can change substantially. Swapping from horizontal to vertical with an L bracket avoids all that. And of course the heavier & larger the camera/lens the more pronounced the effect. Add a vertical grip, and the problem grows.
Can you live without it? Of course.