With no storage limits, it makes more sense to upload your photos and videos automatically from the OneDrive app for Android instead of Google Photos. Then, when you want to show your latest pics from a family trip, you've got easy access to Chromecast and no worries about running out of online storage space. You could even try to have both apps upload your photos for added redundancy and the advantages of both services.
It's encouraging to see how wholeheartedly Microsoft is embracing the various features of differing ecosystems. The Chromecast feature follows other changes to OneDrive for Android. In May, Microsoft rolled out basic Android Wear support with a watch face that shows a selection of your photos on OneDrive from the last 30 days. More recently, Microsoft made OneDrive for Android a lot more full featured, with the ability to open links and stream videos inside the app itself.
The impact on you at home: Right now, Chromecast support appears to be an Android-only feature. The iOS version has yet to receive the same feature and not even Microsoft's home platform, Windows Phone, has Chromecast support for OneDrive. Once Microsoft has OneDrive Chromecast support worked out on Android, an iOS update could be in the cards. As for Windows Phone, if we'll see it all it would be closer to the end of the year after Windows 10 for mobile rolls out.