Advertisers often monitor PPL to measure the effectiveness of certain ads. By comparing the average revenue per lead to the PPL cost, the advertiser can determine if the ads are increasing or decreasing profit. For example, if a the average return on a lead is $0.80 and the PPL is $0.50, there is an average profit of $0.30 per ad. However, if the average return is less than $0.50, the ads should be modified or stopped since the leads cost more than the revenue they are generating.
"PPL" is also used in online chat as an abbreviation for "people."