What's in it for me? Why should I visit your website? These days, if you can't answer those questions (because your users are surely asking them) then your web strategy is in trouble.
Our clients want to know 'how can we make the web work harder for us?' It's both a simple and a complex answer but ultimately it all boils down to value and what incentive or reasons you are offering your users to visit your site.
Just ask Jack Allsopp, or Just Jack as he's more commonly known. Obviously talent has a certain amount to do with his success but Jack and his people also understand the value of giving visitors to their website something that they want. Jack fans who visit his site can download a free mash-up of four of his tracks. Because the tracks (and the mash-up) don't appear on the album, Jack's not losing any money through people choosing to download the free tracks instead of the album, but he is giving visitors to his site something that they value.
And it's not just a one-way thing. As well as giving his fans the opportunity to download new tracks and remixes, Jack offers visitors to his site the chance to have a go themselves, to interact with his content and to share what they come up with. The guys behind the site actively encourage users to take ownership of the content and invest their time into creating and sharing something that they feel proud of.
It may seem counterproductive to give away a free version of the thing you're trying to sell, but the buzz you create around a product by doing this is the best PR you can get and drives people who already like your stuff to your site. I wonder how many of the people who downloaded the free mash-up go back and buy the official version? My bet is quite a few.