ERC-1155 defines a common interface for a contract containing multiple token types. Each token ID has its own balances and can have its own supply and metadata. The design can represent fungible items, unique items or other configurations without deploying a separate contract for every type.
IDs and quantities work together
A game could assign one ID to interchangeable potions and another to a sword issued only once. An account might hold five units of the potion ID and one unit of the sword ID. Having an ID does not automatically make every unit unique; quantities within the same type can remain interchangeable.
Moving several types at once
Batch transfers move multiple IDs and amounts through one operation in the same contract. This can reduce repeated transaction overhead, although actual gas savings depend on the implementation and workload. Contract recipients must implement the required reception behavior for standard safe transfers.
Permissions and implementation risks
The standard's operator approval can authorize management of all the holder's token types in that contract. It should not be mistaken for permission over only one displayed item. ERC-1155 itself does not guarantee immutable metadata, a fixed supply, authenticity or any particular market value.