Why I need an act method etc. in rspec spies

rspec-spies-etc.rb

# new DSL:
# 'act': specifies the action under test as a block
# 'result': the return result from 'act'

describe MyClass do
  subject { MyClass.new }
  
  describe '#method' do
    
    act { subject.method }
    
    before :each do
      subject.stub(:meow)
      
      # Can't put the MyClass#method call here because it will be executed before the inner before :each below
    end
    
    it 'should have called meow' do
      
      
      result.should == 123456
      
      subject.should have_received(:meow)
    end
    
    context 'something global needs changing' do
      before :each do
        # this has to be executed *before* the *act*
        Something::GLOBAL = 'Something different for the purposes of this test'
      end
      
      it 'should not have called meow' do
        subject.should have_received(:meow)
      end
    end
    
    context 'when calling with false' do
      # this act statement takes precendence over the previous
      act { subject.method(false) }
      
      it 'should behave differently when call with false' do
        pending "etc."
      end
    end
  end
end