What's the difference between streaming the content or downloading it in regards to data usage? If it's the same then I don't see the relevance.
The greatest advantage is if your Internet service is sub par and you have buffering with streaming content. This will get rid of the buffering.
Also it allows for the possibility of less video and audio compression. On BBC iPlayer for instance, the audio streaming bit rate is 320 KBS, for the Proms TV broadcasts, but in download it is 640 kbs. With AAC+ and MPEG DASH that is as good a BD in my opinion.
It is interesting that Netflix CEO has been heaping praise on BBC engineering for iPlayer, and acknowledging their innovation and leading the way with the streaming and downloading of media.
As usual though for reasons Netflix can not understand, the BBC have made their work open to all. This is what happened when the BBC developed the first digital volume control and mixer. They have never collected a cent in royalties. They just published their work and incurred the wrath of Margaret Thatcher over it.
In the world of audio and video, most have no idea of the deb owed to the BBC. It was nice to see the Netflix executives acknowledge it.
I'm sure that the download service will be based on BBC technology.
If you are going to Download however you will need something other than just a streaming device like ROKU. You will need something with memory, like an Intel NUC
I have tried to draw peoples attention to the Intel NUC, but to no avail. That device should be on all members Christmas list.