Never. In most cases (Born This Way, Red, ARTPOP) I listen when they leak...
I listened to the previews of Beyonce beforehand, and watched several of the videos online. I didn't have money on my iTunes account that night, so I couldn't buy it immediately...
I think I bought Speak Now without hearing the full album first. But I knew Mine, Sparks Fly, Back To December, Mean, Innocent, Speak Now before the album release (most of those songs were promo singles), and listened to the previews of the other songs...
I refuse to listen to the new classic snippets and I was so shocked to see a full beyonce album late at night out of nowhere that I bought it instantly.
None. I don't want to risk losing my hard-earned money with a potentially bad album. I try to listen to at least a song or download the whole album illegally first. I'd only do it if it was sold on a very high discounted price.
