speed: The blockchain is updated only every 10 minutes and you need to wait for even longer if you want to be 100% sure a longer fork won't show up.
cost: bitcoin miners must spend enormous amounts of energy in an inefficient process in order to keep the network running. Right now, most of the mining costs are covered by the bitcoin bounty that is awarded to miners that successfully mine a block but this reward decreases with time and eventually and transaction fees will have to increase to compensate.
cost: bitcoin miners must spend enormous amounts of energy in an inefficient process in order to keep the network running. Right now, most of the mining costs are covered by the bitcoin bounty that is awarded to miners that successfully mine a block but this reward decreases with time and eventually and transaction fees will have to increase to compensate.