What is your incoming flight is late? We've used the transit desk when continuing on TAM or Gol from an international flight, but only with the whole trip purchased together. Seems logical that you could use it even with separately-purchased trips but I am not positive. You could be sent upstairs to the regular check-in counters and have to pay domestic flight baggage fees which you would not have to pay if both flights were purchased together (note the weight allowances for domestic fights are very low). Remember that you still have to go through security before going to the gate for your domestic flight.