Actually it won't make a difference.
Under the old system, a boss would drop 4 or 5 items that would be split among 25 people. With the current system, everyone has an individual chance for loot which means that 3 shamans and 4 paladins may very well each get that shield they need.
It is also mathematically possible that all 25 people in the raid get an item from one boss and that the next boss has no loot for anyone.
With the old system, you not only had to hope that the item you needed dropped in the first place, you also had to roll against many people to get it. We were hearing a lot of feedback that the need/greed system was being used incorrectly by people that didn't actually need items, but pressed Need anyway. This new system takes that factor out of the equation completely.
Yes, it does mean that you will occasionally get an item you already have—think of this as winning something that no one needed with a Greed roll—but it also means you'll never lose an item you need to someone who doesn't need it, as happened previously.