I don't think leaks do anything other than create buzz (either positive or negative) about an album. If people want to pirate music, they'll do it no matter if it's before the release date or after. When an album leaks, I can see how that's frustrating to an artist, but the people who buy records will still buy them.
I can agree with most of that. I have a self imposed system when it comes to purchasing/downloading music. It's just something that has developed over time and I more or less stick to it.
If it's a band I love, I will listen to no more than 3 singles leading up to the record's release. I will, inevitably, purchase a physical copy of the album on release day. I never listen to leaks, band streams, or anything of the sort. I want the first time I hear the record to be when I pop in the CD.
If it's a huge, major label artist with millions of dollars and airplay every seven seconds, I'll probably listen to a leak, check it out on Spotify and then, if it really strikes a chord with me, purchase it (for example, The 20/20 Experience and Yeezus thus far this year)
Then there are bands I know very little about and simply can't justify spending money on their record until I familiarize myself with them. It happened with Letlive. this year, for example. They streamed "The Blackest Beautiful" really early, so I checked out the YouTube stream and thought I might like it. Then I caught their set at Warped Tour and enjoyed it. The following week, I listened to the record on Spotify a couple of times and then purchased a physical copy that week.
Once I've bought a band's record, they're automatically on my radar for the next record cycle, making them a likely candidate for the first category I talked about.