use mappings inside structs in solidity

After including a mapping inside a struct, when trying to pass the struct into a function, it has to be "storage" instead of "memory". (the "checkBalance" function is just an example here)

1. Is it a good practice to store mapping inside struct?
2. Any alternatives to the mapping type inside the struct? Thought of using array but it has to do the iteration to find the item.

library MappingLib {
    struct Balance {
        uint256 value;
        mapping(string => uint256) positions;
    }
    
    function checkBalance(Balance storage balance, string memory key) public returns (uint256) {
        return balance.positions[key];
    }
}