Fees are in practice a sum of money or cryptocurrency that is withheld by the manager of a service as consideration for the provision of a service.
They are often applied by exchange sites, when buying or selling cryptocurrencies: fees, in this case, represent the cost of trading.
But there are also online electronic wallets or microwallets which, although free when registration, charge a fee both in case of deposit and transfer: in this case fees are the only source of income for these online wallets, since the service is generally provided free of charge.
But there are also fees in simple electronic money transactions. They are referred to as "blockchain fees" or "miners' fees" and represent a kind of transaction fee charged to users who carry out transactions. The payment of this fee represents the reward for cryptocurrency miners who contribute to the existence of the blockchain and have the task of confirming transactions, undermining the blocking of the network where they are located. The higher the fee paid by the sender, the faster its confirmation by miners will be: this commission therefore allows you to accelerate cryptocurrency transfer operations, slowed down by the high congestion of the network. In 2017 the fee for a transaction on the Bitcoin network, for example, was about 300 satoshis/bytes, which is now lower thanks to the adoption of the Lightning Network.
Finally, there are also some faucets themselves who apply a commission as a percentage of the sum requested at the time of withdraw. Fortunately, the faucets that apply these fees are very few and, in any case, almost never require more than 10% of the entire withdraw: considering, finally, that, although they are still given cryptocurrency tokens, they never represent a real cost for the user.