It depends on what sort of program you're running.
If you've got type-in traffic around a popular site, and that site has an affiliate program that works in <iframes> or forwarding, then just use that. It's where the people wanted to go in the first place, so you may as well make your percentage off it.
It's almost effort free, really.
Some of the programs I run DO require a little legwork to get going, but it's still less than making a site presentable enough to flip, and for some I figure it's worth keeping simply because I'll make more in 3 years then if I'd flipped it (I like to think longterm, as I know there'll be market demand for those ones... They're not churn-n-burn).
The stuff that I know won't last too long (like a couple WYD campaigns I a fortnight ago, which basically dropshipped LandOverBaptist stuff) get enough traffic and inbound links to make them worth flipping off elsewhere.
The idea that you need a mailing list, or opt ins, is real in-the-box thinking for affiliate marketing, and really has that pointy headed eBook mentality, in my way of thinking.
Hell, thanks to the prevalence of ways to get people to go online from their phones now, aff marketing is really starting to become a more and more viable thing if you're clever and don't stick to sticking money in your shoe *cough*