From Diablo Wiki
Diminishing Returns is a term used for bonuses that become less of a bonus with more points placed in them. If the first point in something adds 50%, the next 25%, the next 10%, the next 5%, and so on, those are diminishing returns.
Numerous skills and bonus properties worked that way in Diablo II, which forced players to do some math as they weighed where to place their skill points and made other game decisions. The value returned from more Magic Find equipment was a good example, and a table showing can be seen below.
|Magic Find||Rare Find||Set Find||Unique Find|
As you see, adding more and more Magic Find was not very valuable, in terms of finding more Uniques. Unique MF gained nearly as quickly as the others up to about 100% MF, but past that the returns diminished greatly. At high levels of MF, the improvement from even a considerable gear upgrade made little or no difference in terms of increasing the odds of finding more Unique items.
Diminishing Returns in Diablo III
Though it's impossible to know this far in advance, it appears that diminishing returns will not be a major part of Diablo III.
- Clvl Req: Under 10 for all classes.
- Description: Increases a character's willpower.
- Max points: 5
- Rank One: +20% to willpower.
- Rank Two: +40% to willpower.
- Rank Three: +60% to willpower.
- Rank Four: +80% to willpower.
- Rank Five: +100% to willpower.
- Lore: Not yet known.
Jay Wilson spoke about traits from Blizzcon 2010 and said that they were meant to be substantial, valuable bonuses. Not +1% damage type things, but big bonuses that would always make a marked difference in the game play. Whether this philosophy will prove viable in all sorts of game stats isn't yet known.