Other than what hotel mode has said the only difference is how much inflight rest you get in the bunks, 2 man, obviously none and those routes are limited to sectors of up to around 7-8 hrs.
3 man, the majority of trips on the jumbo, gives you around 3-3.5 hrs rest,the "heavy" crew member usually taking the first break from shortly after t/o and then on duty for the rest of the flight until around an hour before landing when the operating crew take over again for the landing.
4 man, at the moment HKG, SIN, GRU, BKK only, 2 full crews, its up to the operating crew exactly how they want to work the rest but its usually around 6hrs rest for each crew.
Who does what is all rostered and you soon get a personel preference as to whether or not you prefer being heavy inbound or outbound, that said its not uncommon for guys to swap around at the briefing stage.