Specifically, I do not find a benefit to this:

    describe Signup do
      describe '#save' do
        it 'saves the user to an organization' do
          # ...
        end
    
        it 'saves the organization under an account' do
          # ...
        end
      end
    end

And I'd rather see this:

    describe Signup do
      it '#saves the user to an organization' do
        # ...
      end
    
      it '#saves the organization to an account' do
        # ...
      end
    end