They can only be bought in minimum quantities (e.g., 4 tokens for €10), and they usually cannot be sold back or used again. At the end of the event, each €2.5 token is worth €0.0.
Drinks are sold for odd numbers of tokens, e.g., 1 token for a beer, but 2.5 tokens for a glass of wine. Beer and wine is 3.5 tokens and you're left with 0.5 tokens of useless.
Tokens are sold at a different place than food and drinks. People who do not want to stand in too many lines tend to by too many tokens -- just in case -- but those extra tokens are worth nothing later on.
Tokens make it harder to see when you're getting ripped off -- like paying €5 for a 500 ml bottle of water (only €10,000 per m^3! such a deal!) -- at an event that does not have any other sources of water (except temporary taps near toilets that are labeled "not for drinking") and does not allow you to bring water in with you.
Vendors claim that:
- tokens save people time when buying drinks, but that's not true when you have to pass through two lines and need to make "token change."
- tokens reduce theft by food staff, which is true for them, but not for customers who are left with useless tokens at the end of the day.
- tokens reduce the risk of robbery, but they concentrate money at locations where tokens are sold.
- make it easier to buy things, but that's only true when they charge even prices in tokens and odd prices for cash. Those numbers can be moved around.