It's advertising a contest associated with one of the most popular bands right now, but it's free to enter, no purchase required.
So it does need to be people who are interested in the band but they don't have to buy anything just enter to win.
So I guess I want something above garbage traffic, but don't have to worry about conversions.
I have a "free" site, ie visitors rarely part with money to access the materials I provide.
But I do want to measure the effectiveness of the (AdWords) adverts I run to get people to the site.
So I measure a "conversion" as user "stickiness", ie staying around to look at a few specific pages rather than doing the normal "run for the hills" in-and-out of a typical search-engine user.
That sounds to be a low barrier, as low as your "enter to win", but I do get useful information.
And in any case ALL of this information is at best a sampling since people turn cookies off, come back 6 weeks later after the cookies have expired, etc.
Rgds
Damon