I think it's far more useful to give the player a broad description of the effects of the item, rather than a precise mathematical breakdown of how the computer implements it.
This is for several reasons:
1. There is no better way to utterly shatter immersion in your game world, unless the entire point is math centric. As soon as you start showing the "man behind the curtain" --- in this case, the math formulas the computer is using to evaluate damage --- you destroy the mystique you're trying so hard to create. Instead of having the "Legendary sword forged from the heart of the Gods and bathed in the tears of Angels" you now have the players thinking "Sword [600+a.atk*10-b.def*4 50].max" because the math would completely eclipse the descriptions.
I know Final Fantasy IV wouldn't be nearly as much fun if each weapon said "Dark Sword: [20+a.atk*4-b.def*2 1].max" or something similar.
2. This "more information" would only overwhelm the player. I'm very good at math and it would overwhelm and annoy me --- I didn't start playing an RPG to have to work out formulas to see which weapon is better.
3. What exactly would you list if you, say, added buffs, debuffs and other things like elemental damage? Your descriptions would start to look like partial dumps of the program.
4. Finally, if you need to tweak items for game balance, every single time you'd need to go edit the description as well.
Let's say I were making a futuristic hacking cyberspace type game. Now, since it is key to the storyline and game world, I would show the player SOME key data. But even then, it would be brief and not so precise that the player has to pull out a calculator. It would be something like: "Upgraded Mk II Cyberdeck, +20% RT, +10% DS" where "RT" = "Response Time" and "DS" = "Defense Strength."
What also is fair is having, say, the Item select screen show how equipping an item changes the player's stats. There, the system is doing all the math and just showing me "OK, this grants +5 AGI, +3 MDF" This is good information to have and helps the player decide, without putting too much technical information on display.