I originally understood the digitization process of Tron/Tron: Legacy to create digital representations of the users, but now I'm not so sure (especially since Sam is shown to bleed on The Grid).
After Sam reunites with Flynn in his hideout, he sits down for a meal with Flynn and Quorra.
Similarly, programs are shown drinking at the End of Line Club.
If the Users are actually physically transported, it makes sense that they may need to eat or drink - but what about programs and ISO's? Do they need to eat or drink?