Parental controls for certain accounts. Content is only available to the account that purchased it on XboxLive. I know PSN had "issues" with someone buying DLC, letting multiple people log in to the account that purchased it, redownload the DLC, then simply remove that account from their PS3. They still have complete access to this content. Saves are stored via individual account, especially cloud saves. Stats and leaderboards are tied to one ID. I wouldn't let a child play on a high ranked SFIV account. (Not that I have one. I am not an online warrior.)
There are multiple reasons be able to have multiple accounts on a system. Why are there multiple user accounts on Windows? If you say backgrounds / themes I'm just gonna laugh at you.
Someone doesn't know how to read. This was NOT about having multiple accounts on a system. I have 3 accounts on my PS3 right now. One for Japan, one for Europe and one for North America.
This was about being able to have two different accounts logged in at once.
Way to miss the buss.
As for the achievements thing I was talking about the possibility of both players gaining an achievement which honestly has zero bearing on whether a game is good, fun, or a big steaming turd in a box. In multiplayer, especially local multiplayer there is zero drive to get a trophy or achievement to me. Even single player I don't care. To get a trophy the developer often assumes you play a certain way. I play my own way.
The worst thing to come from achievements and trophies is giving them away for plaything through the game normally. Get to mission 2? Get achievement...ugh. The whole point of playing the campaign is to get through each mission.