Only full node clients like Bitcoin Core require longer synchronization times. Technically, synchronization is the process of downloading and verifying all previous Bitcoin transactions on the network. Some Bitcoin clients need to know all previous transactions in order to calculate the available balance of your Bitcoin wallet and complete new transactions. This step is very resource-intensive and requires sufficient bandwidth and space to store the entire blockchain. In order to maintain the security of Bitcoin, enough users need to use full node clients because they play the role of confirming and relaying transactions.
