Random numbers play a large role in any computer game. They are key to many game mechanics to introduce variety in feedback.
Some games however take it too far and randomize too much. If you play many rogue likes then you are used to this randomness of loot and dungeon layouts: these games randomize the dungeon floors and all loot.
The dungeon layout works in this case as its part of the global feedback: you enter a dungeon which leads to hell and if you die you have to start from scratch. Would the dungeon be identical every time you start over then you would be bored real quick. To prevent this the dungeon layout is random.
This doesn't work for all games however. People love to talk about exploration and their findings. So in World of Warcraft there are hundreds if not thousands of sites listing the maps and loot tables of the dungeons.
Lesson: if multiple of these sites exist then there is a demand. If there is a demand then the overall mechanic works nicely.
Note: you won't find any of these sites about Diablo with the exception of items.
But regarding items in Diablo here is the thing: if you look for epic items it doesn't matter which boss monsters you kill. The drip chance is random, the item in question is random. So you simply farm any monsters you find and sell your stuff in the auction house - the rewarding gold you spend on items - guess where - in the auction house. Basically the auction house becomes an item shop supplied by random drops of players.
This undermines the exploration, the reward to have killed a specific monster and finally your favorite epic drops. Worse: if the player realizes that all drops are random then the content you supply doesn't matter anymore - as items can be found anywhere. You could theoretically limit your game to one zone and boss - of course I over simplify.
Generally randomness should not give only random rewards. Randomness should introduce variety to feedback, not generate random feedback.
Next up: how to use random generators effectively in games.