Most designers seem to have no problem proliferating the variety of items and their uses to extreme numbers. There are some pitfalls to avoid here, and some good reasons to keep your plethora of items in check.
1. Cost of goods: in boardgames this is more obvious, as the cost of physically producing the parts of the game quickly limits the number of items the game can contain. In video games this comes into play in two ways. Computer memory used to be an issue, but is not really a problem for modern games. Art costs, on the other hand, are probably now more significant. Many games get around this by using the same art piece for several items, often with a different color pallet on the same picture or 3D model.
2. Player loot management: In board games, the players have to organize the little pieces, count them, and move them around during play without losing them. Intentional and unintentional miscounts can be an issue if too many pieces are exchanged too often. I find this particularly troublesome when there are several interrelated exchanges that can take place during the player's turn. Most video game players can name more than one game in which the loot management system was unfriendly. This is largely a UI problem, because the computer can do all of the calculations correctly every time. The Diablo style "loot jigsaw puzzle" is one of the most offensive and difficult to use loot UIs of all time, yet it was used in dozens of games and still persists today as an interface option for designers. Why this persists I cannot explain. The visual nature of it combined with the designer's unwillingness to give up the "realism" of items taking up different amounts of carrying capacity seem to give it staying power despite all the difficulties it causes.
3. Player comprehension: players need to be able to understand and use all the items in the game. If there are too many, it causes problems. Sometimes several items are too similar, and players can't readily keep them separate in their mental model of the game. Sometimes the uses of the items are too trivial and the player loses interest in tracking them. Crafting systems in MMOs are often guilty of this. The designers get so excited about the "depth" and "complexity" of the crafting options that they don't realize they've gone well beyond the average player's ability and willingness to keep track of it all. I would be remiss if I didn't mention Star Wars Galaxies as an example of this. Sure, a few players loved the complexity of crafting in that game, but it drove a lot of players away, or at least away from crafting.
The board game Agricola gives us an example of problems in 2 and 3 combined. Every other turn players must have enough food to feed their family. They need 2 pieces of food per family member they have, unless that family member was added on that turn, in which case they only need 1. Food is one of the items in the game. Also, all three types of animals can be converted into food. Each can be converted at different rates if you have certain other game items. There are also two crops, these too can be converted at various rates if you have certain other items. Also, converting some items is a process that can be done at any time, while others require specific player action. All of this adds up to a difficult planning operation just to make sure you have enough food every other turn. Because the player is trying to plan two turns ahead to have enough food while simultaneously planning what other resources they need to get to craft other things in the game (wood for fences, clay for ovens, and more), it is easy to come up one food short. This combines with lots of little ways to gain and lose resources in 1s, 2s, 3s, 4s, and 5s to maximize the risk of a player ending up with an amount of food that is technically not the amount they should actually have.
When designing loot systems here are some suggestions for things you should consider carefully.
- What is the use for each item? Many video games have loot items that players always sell to vendors for game currency. They appear to have uses, but in reality they do not. World of Warcraft's "greys" are an example of this. Just give the players more currency.
- How many layers of crafting are required to make a useful end product? Players will lose the will to craft if they must turn raw materials into refined materials, then turn those into parts, then those parts into other parts, before finally assembling the second tier of parts into a finished item. This problem can be compounded by having some parts come from different craft skills so that a player can't do everything themselves. FFXIV might suffer from this problem, or at least is on the verge of suffering from it. It's too much for me, but I fall a little on the shallow end of the crafting scale.
- When a player gets an item, will they always know what to do with it? Your items should be easily distinguished. Your items should be evocative of what they are for. Don't get too fancy and fantastical with your item names and art. How many in-game ways are there for the player to find out what they should do with a new item?
- Can players easily and readily access and organize all the items they have? Can you include sorting trays or baggies in your board game? The second edition of Dominion added a strip of paper with all the card names on it, making it much easier to find what you needed in the box. Very few video games include automatic sorting buttons for inventories.
- Do your players have enough room for everything they need to collect? This is often a problem in MMOs where players get a lot of different loot from monsters. If they need to keep too much of it for crafting, and also need to carry around a lot of gear to wear, they'll quickly run out of space. Organization also becomes an issue. More often than not you should reconsider the design of all the loot and crafting rather than simply giving the player more inventory space.
There's a lot more I could say about loot systems and crafting. What do you think about it?