It all depend on what goal you want to achieve. For both growth and sales there are different affiliates who can help you. Before you start with affiliate you should know following things first:
> Ideal customer persona of your product or service
> You have infrastructure ready for growth
> You have a dedicated resource to handle affiliates and their queries
> You have proper finance and accounts setup available.
> Your current churn rate of your service are incredibility low.

Having above things in place you can go ahead recruiting right fit of affiliate partner for your product or service. Yes, having good affiliate partner onboard help you increase growth of your product / website / service.