Is it necessary to wrap the transferMoney method in @Transactional and why?

Yes, the transferMoney method should be wrapped in the @Transactional annotation. This is necessary to ensure the atomicity of the money transfer operation — so that both parts of the transaction (debiting one account and crediting the other) are executed as a single unit. If an error occurs during the transfer, the transaction will be rolled back, and the data will remain in a consistent state, preventing loss or duplication of funds.

Example:

@Transactional
public void transferMoney(Account from, Account to, BigDecimal amount) {
    from.debit(amount);
    to.credit(amount);
    accountRepository.save(from);
    accountRepository.save(to);
}