Keeps associated data together. It also eliminates the possibility of out
parameters not being initialized properly. For example, consider the
following example:

-- some FramebufferManager implementation --

void FBMgrImpl::GetTargetSize(u32* width, u32* height) override
{
  // Do nothing
}

-- somewhere else where the function is used --

u32 width, height;
framebuffer_manager_instance->GetTargetSize(&width, &height);

if (texture_width != width) <-- Uninitialized variable usage
{
  ...
}

It makes it much more obvious to spot any initialization issues, because
it requires something to be returned, as opposed to allowing an
implementation to just not do anything.