Here's some clues about the purposes of The Grid
http://www.youtube.com/watch?v=H4yW3fOrIV0&hd=1
http://www.helloflynn.com/swfs/workserver/hires/ESOR830SYROB.htm
http://www.helloflynn.com/swfs/workserver/hires/BU7YREKD3HD5.htm
Going by these, other materials uncovered by members participating in Flynn Lives, and many of the files on www.helloflynn.com and from what was either shown, spoke of or alluded to in Tron: Betrayal...
The purposes of The Grid:
originally Flynn created The Grid as an experiment to create a "perfect world" that Users and Programs (where Users would actualy go into cyber space itself as a digitized human) could use freely for beneficial purposes, for the free use of and exchange of information in totally perfect, safe, cyberspace digital frontier (remember this was before the the rise of the World Wide Web), also were Users could if they wished, participate in digital games that seem totally real (but would not be deadly...Clu later altered the rules and conditions of the games to make them deadly.)
Also to have a place to build and test simulations of new forms of vehicles, provide a place where other Users could do all kinds of development and research in science and medicine, even make quantum transportation viable.
(from notes in the files on helloflynn.com) Then Flynn thought he might be able to use The Grid, with his genetic algorythms along with his digitized memories of his wife as a template to create a Program based on his deceased wife, Jordan, giving her memories based off of his. (he admited in his notes that he perhaps was being like the character Dr. Frankensten/ sort of like a mad doctor, and maybe he might be going to far to seek such a thing to ressurect Jordan within The Grid...)
He later abandoned that idea after realizing the The Grid was no place for Sam or (any facimilie of) Jordan, it had become too dangerous and wasn't progressing in the way he thought it would..
(most likely noticing Clu's growing militance and the militance of Elite Gaurd under his command... in the time shortly before the coup ).