Getting Paid for Project Referrals (Affiliate Agreements)

1.Have you heard of affiliate agreements (requesting payment for providing referral work)?
2.Do you currently use affiliate agreements (or something similar) in your client contracts?
3.If you answered YES, what benefits do you see in using affiliate agreements?
4.If you answered NO, what are the main reasons for not using affiliate agreements?
5.If you don't use affiliate agreements, which of these would you prefer to receive as compensation for sending a referral?