The box may provide a physical reality for those who enter it, thus explaining what these people do with their time and why their willing to die for the thing in addition to living in motel 6 lodgings. I believe that the box is concentrated but its effects can escape without the user....Jack's dad, kate's horse, walt, whispers, revengeful boar, polar bear, locke's legs, rose's cancer, kim's baby, desmond's gift, and so on.....but it must be special for the physical presence to remain. What freaks Ben out is that this old snowbird from florida showed up with no particular connection to the person using the box and his physical presence remains. This must be atypical, otherwise the others would have a lot of people hanging around and nothing to do with them except feed them to the chickens (see dark meat thread). So, Locke's special communion with the island has bypassed the method used by the others to access the qualities of the island...the so named magic box....and it shocks them. This may have been what happened to Rousseau's companions when they "got sick." Did she describe them as physically sick or did she just shoot them all? What may have happened is that she was the only one unaffected. Big flashback coming there.
Anyway, getting off point. Oh ya, the box. The box allows you to experience or remember any reality....as with Desmond....the only rule is that you can't alter the quantum thread that led you to the island in the first place. That would set up a paradox and would effect the happenings on the island, ergo effecting the lives of the others and changing the course of events unpredictably. Again, as Desmond found, trying to shift quantum outcomes is more difficult that one thinks as realities are straddled alongside one another based upon outcomes. You can try to win her back, but you'll get smacked in the head by a crickett stick or you'll die in a taxi cab.
Only a fool is enslaved by time and space lies at the heart of the box question....what would be required of one who was not? He or she could not be flawed and could be trusted to enjoy the benefits of the box while not changing others' or their own destiny. Every flashback has been constructed to show us the flaws of the survivors (except Rose and Bernard who have recently disappeared from the show....overbudget). To be allowed full access to the box, the kind of courage that was shown by the lady in Sajid's recent flashback is required. One must take a searching and fearless moral invetory and come face to face with the demon in all of us. The most pure are obviously the children, hence they were on the list and taken early. I can't explain why some from the tail and none from the main section (except Walt) were sought. Better defenses by those aft probably.
Anyway, now we've found out that there is a wizard. It's time to see whose behind the curtain!