re: ATV
The ATV can bring 5.5 tonnes of goods to the station and return back 6.5 tonnes of wastes, to burn in the atmosphere.
MIR was a good example of the little necessity to return large payloads intact to Earth. Of course, the station was loaded with tonnes of things they never returned back but this would change with the ATV and the Japanese HTV. What the Russians left aboard Mir were no more used scientific equipments or souvenirs often left by foreign cosmonauts.