Yes off course it is necessary. Your fees are break up of few things which are mostly mentioned in the FAQ section of each exchanger, wallets or from whatever you are cashing out.

For all the wallets and exchangers when you send the coins over the network then specific fee is taken on the behalf of miner, called as miner fees. This is not credited to the service provider but given to the miner itself.

When you do any kind of conversion within two currencies over the exchanger then the fees are taken for exchanger itself.

When you cash out from your wallet to the bank then specific fees are taken called as withdrawn fees. These are for the service provider itself as commission or any other way you call it.

Yes its necessary as they have run the business.