Everybody likes free things, and Google wants to go even further in giving users free Play Store credit just for having a Google Cast device. For each one you have, whether a Chromecast or an Android TV, you’ll get $6 in credit. This is meant to an incentive for users to buy more things from the store. They want you to use Google’s ecosystem to purchase and then stream content. Of course, this credit can be spent on movies, magazines, or anything else available. There does not appear to be a limit to how many of these offers are redeemable.
To get started with offers, check out Google’s Chromecast offers page.