My guess is that if at the time of ticketing, the fare were broken so as to have a coach fare on the POA-GIG segment and business class on everything else, this would have increased the total price. You might get lounge access, an additional free checked baggage allowance, or an expedited line since you have a business class ticket on the GOL segment. IIRC you can ask GOL to assign a seat in the front of the aircraft, which could have additional legroom.