The FOAM Map uses smart contracts to enable a decentralized map without a central authority or single point of failure. 

Each time tokens are transferred between contracts, there’s a small fee charged by the Ethereum network, called gas, that fluctuates depending on how busy the network is at that time. 

Approving FOAM in advance helps to avoid more expensive gas when adding and challenging POI. It does not change your balance of FOAM tokens, and allows for fewer MetaMask confirmations and fewer chances that something can go wrong when adding or challenging a POI.