It is easy to generate leads. It is harder to generate leads that an advertiser is happy to pay for. The approval rate is the share of submitted leads that are confirmed as valid, and it tells you more about a campaign than volume or cost per lead ever will.
Across the network the average is 78%. If yours is lower, your manager will tell you which sources or creatives are pulling it down. If it is higher, that is the best argument for a better payout.