Direct response advertisers often consider CPA the optimal way to buy online advertising, as an advertiser only considers the measured CPA goal as the important outcome of their activity The desired "action" to be performed is determined by the advertiser. In affiliate marketing, this means that advertisers only pay the affiliates for leads that result in the desired action such as a sale. This removes the risk for the advertiser because they know in advance that they will not have to pay for bad referrals, and it encourages the affiliate to send good referrals.