Taking surveys isn't the only way you can earn some cash or rewards points, doing referrals can actually give you less work but more pay. Of course this is not going to generate big money as if you've won a lottery, referrals can generate earnings without having to do surveys. You get incentives for every referral you make which usually corresponds to cash and sometimes rewards points.
There are different ways of getting referrals, it can be direct like sending email invite to friends to join and sign up using your referral link. You can also work like an advertising agency in your own ways by putting up banners or links to attract people, this can be a very effective way to invite referrals indirectly.
Referrals is just another way to earn extra bucks but if you can still manage to do surveys, ptc and pay to read then do so.