It can be a good idea, if you place the affiliate banner ads in a place they will be clicked on and the companies you choose to affiliate with are highly targeted to your website's audience. I would also encourage you to launch a pop-up email capture box, offering exclusive deals in exchange for their email address. Then you can send email blasts to your subscribers with the coupon codes that the companies you have affiliated with have given you to promote. This can be an effective strategy to generating affiliate sales with your website traffic.